Hand-considered hypotheses, 5601–5700
Colour chemistry, dispersion, lightfastness, substrate interaction and printing physics, written one at a time. Chromophores and the equilibria they sit in; pigment particles, the dispersants that hold them apart and the mills that make them; fading as a photochemical, diffusive and catalytic problem; what a substrate does to an ink film and what the film does back; and the transfer and fixing physics of printing. Each entry carries the logical form chosen for it, printed above the claim, so the variety of argument can be checked against the text rather than taken on trust. None has been tested; no citation is given because none is being invoked, every quantity offered as an estimate is marked as one, and the textile dyeing items written elsewhere are deliberately not repeated here.
Chromophores and colour chemistry
Extinction misattributed
H5601. A dye solution that departs from Beer’s law is read as evidence of aggregation, but the departure can come instead from the dimer’s extinction coefficient being lower than the monomer’s at the analytical wavelength, so the absorbance falls while the concentration is unchanged. The two explanations separate if the spectrum is followed at a wavelength where the dimer absorbs more strongly than the monomer, because there the departure should reverse sign. As a rough estimate the crossing lies within a few tens of nanometres of the monomer band for a face-to-face stack, which is near enough to be found by a single scan.
Solvent effect collapsed into one scale
H5602. The shift of a dye’s absorption maximum between solvents is indexed to a single polarity scale, yet for a dye whose dipole moment barely changes on excitation the refractive-index term should dominate and the polarity term should nearly cancel. On that reading the scale measures the solvent’s polarisability in disguise. A series of solvents matched in polarity but differing in refractive index would test it, and the differences needed are modest, of order 0.05 as an estimate.
Batch identity disputed
H5603. Two pigment batches carrying one Colour Index number and differing visibly in masstone are usually blamed on particle size, but a batch whose colour changes on milling and does not return on annealing has been converted to another crystal form by the mill rather than dispersed by it. The identity of a pigment is then a polymorph specification as much as a chemical one, and a certificate naming only the CI number certifies very little. Powder patterns before and after milling, with and without annealing, would say which.
Unobserved equilibrium
H5604. An azo dye’s hue is assigned to its azo form when a large fraction of the same solution is the hydrazone tautomer, and the two forms absorb at different wavelengths. What is reported as a solvent effect on hue is then a shift of an equilibrium that the spectrum integrates over. Because that equilibrium responds to acidity, a substrate that supplies protons should move the hue without changing the dye.
Role reversal
H5605. A lake pigment’s permanence is credited to the dye and blamed on the mordant when it fails, but in a lake the cation is the framework: the dye is held as an insoluble salt whose coordination decides whether water and light can reach the chromophore. Aluminium and calcium lakes of one dye should therefore differ in lightfastness for a reason that is structural rather than chromophoric. The test is a series of lakes of one dye with different cations, exposed side by side.
Artefact disguising a mechanism
H5606. Fatigue in a photochromic film is reported as degradation of the molecule, but part of the loss is a fraction trapped in a closed conformation that absorbs where the open form does not. That fraction is recoverable by heat or by prolonged darkness and is not degradation at all. A film cycled until its response has fallen away and then held warm in the dark should recover some optical density if trapping rather than bond breaking is the cause.
Category error in measurement
H5607. A fluorescent dye’s colour in a print is partly emitted light, so a reflectance measurement of it is not the same quantity as for a non-fluorescent dye. An instrument that illuminates with polychromatic light and reads at a fixed geometry can report a reflectance above unity in the emission band, which is the signature of the error rather than a fault in the instrument. The consequence is that a fluorescent ink and a non-fluorescent one cannot be matched from reflectance data alone.
Geometric explanation preferred
H5608. The hue shift seen when a dyed film is stretched is read as a change in the dye’s environment, but drawing orients the transition dipoles and changes the component of polarised light that each absorbs, which moves the apparent band without moving the transition energy. The two separate because orientation changes the band with polarisation while a true spectral shift does not. A stretched film measured at two polarisations, before and after annealing, would show which of them moved.
Two instruments, one event
H5609. The hysteresis loop of a thermochromic pigment is usually credited to the pigment, but in a leuco system the loop is set by the melting and freezing of the solvent or fatty acid around the dye, so its width is a calorimetric quantity in colorimetric dress. A calorimeter run at the same rate should show transitions at the same two temperatures, which would name the loop’s owner. If the two disagree, the colour change is not the melting it is said to be.
Host-owned kinetics
H5610. The fade and recovery of a photochromic dye in a polymer is modelled as the molecule’s own kinetics, but in a rigid matrix the rate is set by the free volume and the oxygen around it, so the intrinsic rate is never observed. The activation energy from such a fit belongs to the matrix’s relaxation rather than to the isomerisation. The same dye in two matrices of different glass transition should give two activation energies that follow the matrices.
Undefined quantity
H5611. Indicator dyes are calibrated in water and then used to report the acidity of a coating, where the dielectric constant, the ionic strength and the solvation all differ, so the number they report is a pH only in the operational sense of that film. The claim is not that the measurement is wrong but that the quantity is undefined away from its calibration medium. A film holding two indicators of different charge type should report two different acidities if the effect is real.
Nucleation control
H5612. Whether a quinacridone mill gives the red or the violet form is attributed to milling temperature, but the deciding event is nucleation: a trace of the unwanted form surviving the mill seeds its own growth, and temperature only changes how fast the seed wins. Batch-to-batch colour variation is then a contamination problem rather than a thermal one. Seeding a clean batch deliberately with a little of the other form should reproduce the failure at the ordinary temperature.
Band-limit argument
H5613. A metameric match fails under a new illuminant because the two reflectance curves cross, and the failure is often blamed on the observer. But a match built from three samples of the spectrum cannot be better than the sampling allows, and the mismatch under a source with a narrow line is set by the width of the object’s absorption bands relative to that line. Where the bands are narrower than the instrument’s interval no observer would see the match hold, so the mismatch is a resolution limit rather than a defect of colour vision.
Instrumental inversion
H5614. The pressure dependence of a dye’s absorption maximum is a nuisance in high-pressure spectroscopy, but in a polymer film it can be turned around and used as a manometer, because the shift is nearly linear in hydrostatic pressure over a useful range. The film then reports the pressure it is in, with a spatial resolution set by the optics rather than by the transducer. A film calibrated in a pressure cell and then applied to a loaded surface would show whether the sensitivity survives the application.
Transient intermediate
H5615. Bleaching a coloured dye with hypochlorite looks like a one-way destruction, yet the first step is often chlorination of an aromatic ring and the chlorinated product can be more coloured than the starting material. A bleach bath can therefore darken a stain before it removes it, which is misread as resistance. Following the absorbance at short times, before the bleach is quenched, would show whether a coloured intermediate appears.
Minority species rate control
H5616. The photofading of an azo dye is modelled on the azo form, yet the hydrazone tautomer present in small proportion can be the species that absorbs the damaging photon, because its absorption extends further into the ultraviolet. The rate then tracks the tautomer ratio rather than the total concentration, which would explain why two dyes of similar colour fade at different rates. A series of solvents that shift the ratio without changing the dye should shift the fade rate in proportion.
Optimum with a bound
H5617. An optical brightener raises a substrate’s whiteness only up to the concentration at which its emission is reabsorbed by neighbouring molecules, beyond which it acts as a dulling absorber. The optimum is set by the overlap of its absorption and emission spectra rather than by its solubility, and it should move to lower add-on as the film thickens. Films of increasing thickness at one add-on would show the optimum shifting, which distinguishes reabsorption from simple saturation.
Component misattribution
H5618. The cooling performance of a dark roof coating is credited to the pigment’s near-infrared reflectance, but in a thin film a substantial part of the absorbed energy is taken up by the binder, whose absorption in that region is not negligible. A pigment swap at constant binder can therefore improve the number by less than the pigment’s spectrum promises. Two binders of different near-infrared absorption at matched pigment loading would separate the contributions.
Crossover between two contributions
H5619. The red of a gold colloid is assigned to the plasmon resonance, but at the smallest sizes the interband transitions from the d band overlap the plasmon and damp it, so the colour’s movement with size is not a pure plasmon effect. The two contributions cross over at a size that depends on the metal and on the surrounding medium. A size series measured across a solvent change would show the crossover as a change in the direction, not only the magnitude, of the shift.
Phase separation as the hidden step
H5620. An ink that clouds or throws a deposit on cold storage is described as unstable, but the event is often the crystallisation of a dye-surfactant complex whose solubility falls faster with temperature than either component’s alone. The deposit is a phase rather than a degradation product, and it redissolves on warming. A cold-stored sample warmed slowly and watched for redissolution would show the reversibility that degradation would not.
Pigment particles and dispersion
Instrument measures compliance
H5621. The fineness-of-grind gauge is read as a particle size, but the reading is the depth at which the paste’s yield stress is exceeded by the blade’s pressure, so a flocculated paste reads coarse and a well-dispersed one of the same size reads fine. What the gauge certifies is a rheological state as much as a dimension. Reading one paste at two blade loads, against a sedimentation size, would show the reading moving with load.
Wrong variable selected
H5622. Steric stabilisation is specified by the graft polymer’s molecular weight, but what decides flocculation is whether the grafted chains are soluble in the continuous phase, which is a solubility-parameter match rather than a chain length. A long stabiliser in a poor solvent collapses and fails while a short one in a good solvent works. A series of dispersants sharing one anchor group and varying only side-chain solubility would put the collapse at a solubility boundary.
Dilution changes the answer
H5623. Zeta potential is measured on a diluted suspension because the instrument requires it, while the ink that must not flocculate is concentrated and has a much higher ionic strength. The potential governing stability in the can is therefore not the one reported. Measuring at several dilutions and extrapolating to the ink’s own solids would show whether the ranking of two dispersants survives the extrapolation.
Non-monotone dose response
H5624. Adding dispersant to a pigment paste improves stability to a point and then worsens it, and the worsening is called overdosing without a mechanism. The likely mechanism is that excess polymer forms a second phase or micelles that bridge between particles instead of separating them, so one molecule acts as both stabiliser and flocculant. A dose series watched for a low-shear viscosity maximum would show the two regimes.
Side reaction inside the process
H5625. Bead milling is scaled by specific energy, but part of that energy heats the slurry and part of the heat drives desorption or hydrolysis of the dispersant, so a run that delivers the right energy at the wrong temperature delivers a different product. The size that comes out reflects the dispersant’s survival as much as the mill’s work. Running one energy dose at two temperatures, with the dispersant analysed afterwards, would separate the two.
Geometric artefact in a strength test
H5626. Tinting strength is compared by drawdown, but the film thickness of a hand drawdown varies by more than the batch differences being judged, so a strength ranking can be a thickness ranking. The quantity wanted is extinction per unit thickness, which requires the thickness to be measured rather than assumed. Drawdowns at a known gap, weighed before and after drying, would supply the thickness and expose the artefact.
Optimum displaced by crowding
H5627. Titanium dioxide scatters best at a particle size of order half the wavelength of light in the binder, an estimate that moves with the binder’s index, but at the loadings used in real paints the particles crowd and the scattering per particle falls, so the best loading is lower than the best size would suggest. The hiding-power curve therefore has a maximum in loading that is not a maximum in size. Hiding power across a loading series at fixed size, and across a size series at fixed loading, would put the two maxima in different places.
Mechanism differs from appearance
H5628. Extenders are added to reduce cost, and the opacity they sometimes add is explained as dilution of the titanium dioxide, but the effect is the opposite: the extenders hold the scattering particles apart and reduce their mutual shading. The mechanism is a spacing effect, which is why an extender of the wrong size can make a paint less opaque. A series at one titanium dioxide loading with extenders of several sizes would show opacity following spacing rather than loading.
Percolation threshold
H5629. Gloss collapses in an emulsion paint at a pigment volume concentration treated as a formulation constant, but the collapse is the point at which air voids connect through the film, which is a percolation threshold rather than a chemical one. That makes it sensitive to the pigment’s packing geometry and nearly insensitive to the binder’s chemistry. One binder with pigments of different shape should show the threshold moving with the packing.
Overshoot beyond optimum
H5630. Beyond monolayer coverage of a pigment, dispersant that is not adsorbed stays in the continuous phase, where it plasticises the dried film and lowers its block resistance. An ink dosed for dispersion stability can therefore be dosed past the point where the print’s mechanical properties suffer, and the two optima do not coincide. Measuring the free polymer in the serum beside the film’s hardness would show the excess arriving before the hardness falls.
Cross-component interaction
H5631. Two pigments that are each well dispersed can still drift in colour on storage because their surface charges are opposite and the pair co-flocculates, which no single-pigment stability test can reveal. The drift is a property of the mixture and cannot be predicted from either certificate. A stored mixture sampled alongside its two components would show hetero-aggregation appearing where neither component alone did.
Timescale mismatch
H5632. Nanomilling creates fresh surface faster than the dispersant can adsorb onto it, so the size at the mill exit is set by the ratio of adsorption time to residence time rather than by the energy alone. A mill run faster than the adsorption can then make a coarser product than a slower one at the same total energy. One energy dose at two flow rates, with the size measured at the mill exit rather than after let-down, would show the ratio.
Storage as a reaction
H5633. Coarsening of a stored ink is usually put down to coalescence, but the process is dissolution and re-precipitation driven by the solubility difference between small and large particles, so it runs fastest where the size distribution is widest. A narrow distribution can then outlast a wide one of the same mean. Storing two such distributions at one temperature, with the size measured at intervals, would show the spread driving the rate.
Process damages product
H5634. Ultrasonic dispersion is assumed gentle because it works through cavitation in the liquid, but the collapse of a cavity produces local heat and radicals that can attack the pigment surface and the dispersant. A sonicated batch can therefore be chemically different from a bead-milled one at the same size. Comparing the two at matched size, by surface analysis and by fade testing, would show the damage that size cannot.
Surface chemistry sets appearance
H5635. Carbon black’s jetness is attributed to primary particle size, but the blackness also depends on surface oxygen, because quinone and carboxyl groups absorb in the red and shift the undertone from blue toward brown. Two blacks of one size and different oxidation therefore look different, and the difference survives milling. One black oxidised to several degrees at matched size would show the undertone moving with the surface.
Orientation over dimension
H5636. Metallic flake brightness is normally bought with flake size, but the specular reflectance of a dried film saturates once the flakes overlap, and past that point a coarser flake adds sparkle without adding gloss. Two inks differing only in flake diameter should then be indistinguishable at the specular angle and clearly different away from it. That signature, rather than a reflectance value at one angle, is what would tell a coarse grade from a better-oriented one.
Distribution disguised as a value
H5637. An interference pigment’s colour travel is quoted as a single reflection colour, but the colour is set by the thickness distribution of the oxide layer, and a broad distribution mixes several interference orders into a desaturated sheen. Two batches of one nominal colour can then differ in chroma through the width of that distribution rather than its mean. Goniospectrophotometry at several angles, read for the distribution, would show the width.
Geometry of measurement
H5638. A pigment paste’s yield stress is reported from one rheometer gap, but a flocculated network’s yield stress depends on the gap because the network’s largest structural length is comparable to it. The value is then partly a property of the instrument, and two laboratories with different gaps will disagree systematically. One paste run at several gaps would show the plateau where the network is smaller than the gap.
Flow during drying reorients
H5639. Pearlescent flakes in a drying film are carried by the evaporative flow toward the surface, and those arriving last lie at a different angle from those deposited first, so the film has a depth-dependent orientation. What looks like one reflection is an average over that gradient, and the gradient depends on the drying rate. Films dried at different rates from one ink, measured before and after removing the top layer, would show it.
Contaminant as colorant
H5640. Nobody counts grinding-media wear as a colorant, yet the zirconia entering an ink from the beads is a high-index contaminant that scatters, so a long-milled batch can be lighter and less chromatic than a short-milled one at the same pigment size. The colour change is then a wear measurement. Ashing two batches milled for different times, with colour measured on the same drawdown, would show the correlation.
Lightfastness and its mechanisms
Environment-imposed boundary
H5641. Lightfastness is measured on an open sample where oxygen is plentiful, but a print sealed between film and board has a finite oxygen reservoir, and a fade that consumes oxygen must slow as the reservoir empties. A laminate can therefore look more stable than the same ink in air. Exposing one ink open and laminated, with the oxygen partial pressure controlled in the open case, would separate the two.
Dose not a sufficient statistic
H5642. Fading is specified by a dose, but one dose delivered slowly and the same dose delivered quickly can give different colour loss, because a slow exposure allows damaged sites to recover or oxygen to be replenished. The reciprocity failure is a signature of a mechanism with a recovery step. A dose series at two irradiances with the same total dose would show the divergence and its direction.
Protection with a lifetime
H5643. An ultraviolet absorber protects a coating by screening light, but the absorber is consumed by the absorption, so protection decays with exposure and the fade rate rises with time at constant irradiance. A linear extrapolation from early data therefore underestimates the long-term loss. Measuring the absorber’s concentration and the coating’s colour on the same sample at intervals would show the protection falling before the colour does.
Mobility constraint
H5644. Hindered amine stabilisers cycle between an amine and a nitroxide, and the cycle needs the molecule to reach the radical site, so in a film below its glass transition the stabiliser is present but immobile. Its measured effectiveness then reports the film’s mobility rather than its own chemistry. One stabiliser in two binders of different transition temperature should give protection that follows the transition.
Reporter and actor reversed
H5645. When a print on paper yellows the ink is blamed, but the paper’s lignin and residual peroxides are a larger source of chromophore, and the ink’s fade is measured against a background that is itself moving. The colour change of the print is then partly a substrate measurement. Printing one ink on a lignin-free and a lignin-containing paper, exposed together, would attribute the yellowing.
Physical gate on a chemical rate
H5646. Humidity changes fade rates by more than photochemistry alone allows, and the mechanism is probably physical: water plasticises the binder, raises its oxygen permeability and swells the film, so the same photon meets more reactive oxygen. The dependence is on the film’s transport properties rather than on the dye’s excited state. Fade at several humidities, with permeability measured on the same films, would show the correlation.
Catalyst in the film
H5647. Chalking of a pigmented coating is described as the pigment’s failure, but in a film containing titanium dioxide the pigment is a photocatalyst and the chalking is the binder’s oxidation, with the pigment left as powder on the surface. The pigment’s own lightfastness can be excellent while the film fails. One pigment in two binders of different oxidative stability would chalk at different rates, which names the actor.
Metric hides mechanism
H5648. A colour change is reported as one number, and that number can come from a loss of chroma, a rotation of hue or a change in lightness, which have different mechanisms and different remedies. Two samples with the same reported change can therefore be failing for opposite reasons. Reporting the three components separately for a set of faded samples would show them moving in different directions.
Front propagation
H5649. Fading in a thick film proceeds as a front, because the top layer bleaches first and then transmits more light to the layer beneath, so the rate at depth is not the rate at the surface. The depth profile of colour is a moving boundary problem, and a film opaque at the start becomes translucent as it fades. Sectioning a faded film and measuring colour across the section would show the front.
Location decides stability
H5650. Two inkjet papers of different coating type hold the same dye at different depths, and dye near the surface meets air and light while dye buried in a swellable layer does not, so one ink can have two lightfastness values. The difference is a place rather than a chemistry. Printing one ink on a porous and a swellable coating, with and without an overlay, would locate the sensitive depth.
Product of the protection
H5651. An ultraviolet absorber added to a clear coat to protect the colour beneath can itself yellow, because its photoproducts absorb in the blue, so the coat contributes a change it was added to prevent. The protection and the defect are the same molecule. A clear coat with and without the absorber, over an opaque white base, would show the yellowing attributable to it.
Diffusion-limited quantum yield
H5652. Below its glass transition a polymer film has almost no oxygen diffusion, so a dye that fades by a singlet-oxygen route slows not because its photochemistry changed but because the quencher cannot reach it. In that region the temperature dependence of fading should follow a diffusion activation energy, which is much larger than a photochemical one. Fade across the transition, with oxygen diffusion measured separately, would show two activations.
Non-unidimensional scale
H5653. Blue wool standards are used as a scale of lightfastness, but each standard is a different dye in a different wool, so the scale orders mechanisms by their sensitivity to the test spectrum rather than along one axis. A sample can match one standard under a xenon source and another under daylight, and both readings are honest. Exposing the standards themselves under two sources and comparing their order would show the dependence.
Trace catalyst
H5654. Batch variation in a pigment’s lightfastness is assigned to crystal form or particle size, but trace transition metals, at parts-per-million levels that are an estimate rather than a specification, catalyse hydroperoxide decomposition and can dominate the rate. The variation is then a purity specification that no colour data would reveal. Two batches of one pigment analysed for iron and copper, and faded with and without a chelator, would test it.
Spectral overlap bound
H5655. Fading behind glass is assumed prevented by the glass, but ordinary glass transmits the visible and cuts only the ultraviolet, so a dye absorbing in the visible is barely protected while one absorbing only in the ultraviolet is well protected. The protection is bounded by the overlap of source, glass and dye absorption. Two dyes of different absorption edge behind one glass would show the bound.
Reversibility splits the effect
H5656. A faded print that recovers colour in the dark is said to have faded less than it appeared, but the recovery is a separate phenomenon: a trapped photoproduct relaxes or a reduced dye re-oxidises. The total change is the sum of a reversible and an irreversible part, and only the second matters for permanence. Colour measured immediately, after a dark interval and after re-exposure would separate them.
Inverse relation between two virtues
H5657. A dye that is a good sensitiser is a poor candidate for a lightfast print, because the long excited-state lifetime and triplet yield that let it transfer energy to oxygen also let it damage the substrate. Sensitivity and stability are two readings of one property, and a dye cannot be maximised in both. A series ranked by singlet-oxygen yield and by fade rate in an inert matrix would show the ordering invert.
Rigidity as quencher
H5658. The lightfastness of an isomerisable dye rises as the matrix stiffens, because the excited state cannot make the large-amplitude motion that leads to the coloured form and returns its energy as heat. A hard coat can then protect a dye by preventing the very change it was designed to make. One dye in matrices of different stiffness, with colour yield and fade measured together, would show the trade.
Counterintuitive direction
H5659. Aggregated dyes have short excited-state lifetimes because the excitation is delocalised over many molecules, so an aggregate is often more lightfast than the same dye molecularly dissolved, and diluting a dye in a print can lower its lightfastness. That reverses the usual assumption that less dye fades less. Prints of decreasing dye load, with the aggregation state measured spectroscopically, would show fade per molecule rising.
Ranking not preserved
H5660. Accelerated lightfastness testing ranks materials at an irradiance far above service, and a mechanism of higher order in intensity is over-weighted in that ranking, so two materials can invert their order between the test and the window. The test is then a filter rather than a predictor. A small set of samples exposed at three irradiances to the same total dose would show whether the order survives.
Substrate and film formation
Test measures another quantity
H5661. A paper’s absorbency is reported by a water-absorption test, but an ink meets capillary penetration of a liquid whose surface tension and viscosity differ from water’s, through pores that the water test may fill differently. A paper ranked absorbent by the test can be slow for an ink. Timing penetration of the actual ink on the same sheets would show the ranking moving.
Competing effects
H5662. Feathering looks like excessive wetting, but lowering the ink’s surface tension also increases its penetration into the paper, so a surfactant that sharpens the edge can lighten the dot. The two effects pull in opposite directions on one variable. Lines printed from a surfactant series, measured for edge width and for density, would show the curves crossing.
Process variable sets durability
H5663. Latex inks form a film by particle coalescence, which needs the film to stay above its minimum film-forming temperature until the water leaves, and the ink’s humectants lower that temperature while the dryer raises it. Print durability is therefore set by the drying schedule as much as by the polymer. Prints dried fast and slow from one ink, rubbed and washed, would show the schedule’s effect.
Substrate attacks ink
H5664. A print on plasticised polyvinyl chloride fades or blocks because plasticiser migrates into the ink film, lowering its glass transition and letting the surface flow, so the failure belongs to the substrate’s additive acting on the coating. The ink is not unstable in itself. One ink on rigid and on plasticised sheet, with the film’s transition measured after ageing, would show the plasticiser’s arrival.
Mechanism misnamed
H5665. Set-off in a stack is blamed on slow drying, but the transfer to the back of the next sheet is often the vehicle being absorbed into the sheet while the pigment-rich layer stays soft, so the ink is not wet in the usual sense. The remedy is a change in absorption rather than in drier. Sheets stacked at different times after printing, with the transferred amount measured, would show which step limits the rate.
Surface with a shelf life
H5666. Printing on polyethylene requires an oxidised surface, and that oxidation is not permanent, because low-molecular-weight chains migrate into the bulk and bury the polar groups, so the surface energy falls over days. The treatment’s age is then part of the substrate specification. Adhesion tested on one treated film at intervals would show the decay.
Time-dependent surface
H5667. Corona treatment is specified by its watt density, but its effect on wetting decays with the film’s storage temperature and humidity, so two rolls treated identically can print differently. The treatment is a state rather than a finish. Wetting measured on treated film stored at two temperatures, at intervals, would show the decay rate and its dependence.
Oxygen inhibition
H5668. An ultraviolet-cured ink is inhibited by atmospheric oxygen at its free surface, because oxygen quenches the radicals before they propagate, so the topmost layer stays tacky while the bulk cures, and that layer is a larger share of a thin film than of a thick one. The measured tack is a boundary effect rather than an incomplete dose. Films of several thicknesses cured at one dose, with the surface layer removed before testing, would show the inhibited depth.
Hydrolytic bond failure
H5669. Adhesion of an ink to glass is attributed to polarity matching, but the durable bond is a silane or titanate coupling that hydrolyses in water, so failure after humid ageing is a bond-breaking reaction rather than a loss of wetting. The interface degrades while ink and glass are both intact. Samples aged at several humidities, with the failure plane located, would show the hydrolysis.
Length-scale match
H5670. Gloss is not smoothness but roughness at a scale comparable to the wavelength of light, so a coating over a gentle texture of a few micrometres, an estimate of the scale that matters, can stay glossy while a finer but steeper texture scatters. The variable that matters is the slope of the surface rather than its amplitude. Gloss on coatings over substrates of known roughness spectra would show the slope dependence.
Filtration by the substrate
H5671. In a porous substrate the vehicle is absorbed and the pigment is left behind, so the print is more concentrated at the surface than the ink was, and its strength depends on the substrate’s permeability. Two papers of different porosity can therefore give different strengths from one ink at one drop size. A graded series on papers of measured permeability, with pigment load per area measured, would show the filtration.
Substrate emission
H5672. The white point of a print is often set by the paper’s optical brighteners, which absorb ultraviolet and emit in the blue, so the paper is not a passive reflector and its contribution depends on the illumination’s ultraviolet content. A print matched under a source with ultraviolet and viewed under one without will shift. Measuring the paper’s emission separately from the print’s reflectance would separate the two.
Density-dependent parameter
H5673. Dot gain is treated as a fixed property of a press and a paper, but an isolated dot gains differently from one surrounded by others, because spreading is limited by neighbours and the light scattered from the paper is shared. Gain is therefore a function of local density rather than a constant. A target of patches at several screen percentages, each gain measured in place, would show the dependence.
Structural threshold
H5674. A paper coating’s absorption of ink is set by its pore structure, and the pores close at a pigment-to-binder ratio at which the binder fills the voids, which behaves like a critical pigment volume concentration. Beyond it the coating is porous and the ink strikes through; below it the ink sits on the surface. Coatings on either side, with pore size measured, would show the transition.
Bimetal analogy
H5675. Curl in a printed sheet comes from the sheet being a laminate of layers with different moisture expansion, not from drying as such: the curl follows the humidity difference across its thickness, as a thermostat strip bends. The ink changes the expansion on one face. Sheets printed on one side and conditioned at several humidities would show curvature following the difference.
Interdiffusion under pressure
H5676. Blocking of a printed reel is treated as incomplete drying, but two dry printed surfaces can adhere when the binder at each surface is above its glass transition at the reel’s temperature and the films interdiffuse under the winding pressure. The failure is polymer diffusion rather than residual solvent, and the remedy is a harder surface rather than more heat. Reels wound at several temperatures and unwound at one would show the threshold.
Fatigue rather than adhesion
H5677. A finish on leather that peels after flexing is called poorly adhered, but the crack begins at a flaw and grows by fatigue under repeated bending, so the failure is a fracture problem and the peel strength is irrelevant to it. A finish with high peel strength and low toughness can fail first. Flexing finished leather at several strain amplitudes, with crack growth measured, would show the fatigue law.
Contact variation
H5678. Print on corrugated board is uneven because the flutes support the liner at intervals, so impression pressure varies across the sheet and ink transfer follows the pressure. The banding that results has the flute pitch, which identifies it as mechanical rather than an ink problem. Printing at several impression pressures and mapping density against flute position would show the correspondence.
Dewetting criterion
H5679. A water-based ink on a non-porous film can bead rather than film, and the criterion is not the ink’s surface tension alone but its difference from the substrate’s, with contamination by slip additives often deciding it. A film that wets a clean surface can fail with a trace of silicone. Contact angle along a contamination gradient, with print density beside it, would show the threshold.
Hidden chemical environment
H5680. Archival printing requires neutral paper, and the usual test is the extract pH, but the acidity that matters is the acidity at the ink’s interface, buffered by the coating’s calcium carbonate and different from the bulk extract. A paper that passes the extract test can still hydrolyse an ink at the interface. Prints on buffered and unbuffered papers of one extract pH, aged and analysed at the interface, would show the difference.
Printing physics and ink transfer
Dimensionless grouping
H5681. Satellite drops form behind a main drop when the ligament pinches in two places, and whether it does is governed by the ratio of inertial to capillary force at the pinch, with viscosity delaying the pinch. The satellite’s presence is then predictable from a dimensionless group rather than from nozzle diameter alone. Stroboscopic imaging of one nozzle across a frequency sweep would show the satellite appearing at a value of the group rather than at a frequency.
Energy partition
H5682. The diameter of a dot on paper is modelled as a spherical cap, but the drop’s kinetic energy is spent in spreading, in deforming the coating and in rebound, and rebound should stop mattering above a threshold speed, leaving dot diameter independent of further speed. A plateau in dot diameter against impact speed would be evidence for the partition, and a continuing rise would be evidence against it. Drops of one ink at several speeds, imaged at short times, would show which.
Competition of two flows
H5683. The coffee ring is explained by outward capillary flow carrying particles to the edge, but a pigmented ink also has a return flow, and particles large enough to sediment faster than that return flow deposit toward the centre. The ring’s direction is a competition between two transport times. Dots of one ink at several particle sizes, dried and profiled, would show the deposit moving inward.
Cavitation
H5684. Transfer in a high-speed nip is described as a split of a film, but the split begins with cavitation, because the film cannot sustain the tension the nip imposes, and the voids that open decide how much ink stays on each surface. Transfer is then governed by the ink’s tensile strength at press speed rather than by its low-shear tack. Transfer across a speed range at constant film thickness would show where cavitation begins.
Emulsion stability
H5685. An offset ink absorbs fountain solution into a water-in-oil emulsion, and the greying and poor drying that follow are blamed on the water content, but the effect depends on droplet size: fine droplets are stable while coarse ones break onto the plate. The variable that matters is the dispersion of the emulsion rather than its water content. Emulsions of one water content at two droplet sizes, printed and dried, would show the difference.
Scaling argument
H5686. Gravure cell emptying is a capillary-number problem, so the transferred fraction should collapse onto one curve against that number, but only if the cell’s aspect ratio is held: a deep cell empties by a different route from a shallow one at the same number. Cells of two depths at matched capillary number should then disagree, and the size of the disagreement measures the aspect ratio’s contribution. A transfer series across speeds for cells of several depths would show whether the collapse is real.
Impression as the controlling variable
H5687. Flexographic colour is specified by the anilox cell volume, but the plate-to-substrate impression decides how much of that volume reaches the substrate, so a run at higher impression prints denser with the same anilox. Colour variation down a run is then mechanical drift rather than ink drift. Density logged against impression pressure over a run would show the correlation and its sign.
Shear history
H5688. Screen printing deposits a thickness set by the mesh’s open area, but the ink’s viscosity at separation depends on the shear it saw under the squeegee, so one ink at two angles or speeds gives two deposits. The deposit records shear history rather than the screen. Deposits printed across a speed and angle grid, weighed, would show the history.
Charge-limited development
H5689. Electrophotographic density is set by the toner’s charge-to-mass ratio, which the field between developer and photoconductor develops, so a toner that has aged or taken up humidity develops less density although its pigment is unchanged. The drift is then a triboelectric measurement. Density plotted against measured toner charge over a long run would show the relation.
Two-phase dynamics
H5690. In a thermal inkjet nozzle the vapour bubble’s collapse sends a pressure wave back into the channel, and the wave can draw air in at the nozzle, so the behaviour after a pause is set by the channel’s geometry as much as by the ink’s drying. The nozzle recovers only when the bubble is expelled. Imaging the nozzle during the first drops after a pause would show the air’s entry and its clearance.
Synchronisation window
H5691. A continuous inkjet breaks its stream at a driven frequency, and a drop is charged correctly only if the break-off falls within a window relative to the charging pulse, so print quality depends on the phase of the break rather than on the charge’s magnitude. The printer’s phase control is a timing control. Stroboscopic observation across a phase sweep would show the window and the satellites outside it.
Additive decomposition
H5692. Dot gain in offset has a mechanical part, the ink spreading beyond its nominal area, and an optical part, light entering the paper, scattering and emerging from the unprinted surround so the dot appears larger. The optical part is the larger and is set by the paper’s point spread, which is why one set of plates gains differently on different papers. Measuring the dot’s physical area and its apparent area separately would give the two parts.
Saturation
H5693. Colour strength rises with film thickness up to the thickness at which the film becomes opaque, and beyond that the density changes only through gloss and surface reflection, so chasing density with more ink changes the surface rather than the colorant. The film’s opacity is the bound. Density across a thickness series, with gloss beside it, would show the plateau and what changes on it.
Diffusion barrier
H5694. Oxidative drying of an oil-based ink proceeds by oxygen diffusing into the film and reacting with unsaturated bonds, so dry-to-touch is set by the surface reaction while through-dry is set by diffusion, and a film that skins quickly can stay soft beneath. The skin is a barrier to its own cure. Films sectioned at intervals, with hardness at the surface and at depth, would show the gradient.
Two-layer wetting hierarchy
H5695. In multicolour printing the second ink must wet the first, and the criterion is not its surface tension against air but against the first ink’s surface, which changes as that ink sets. A sequence that traps well wet-on-wet can fail wet-on-dry because the first film’s surface energy has fallen. Transfer measured at several intervals between units would show the window.
Transport sets tolerance
H5696. Register error between units looks like a mechanical tolerance, but the paper changes dimensions between units as it takes up water from the ink and loses it in the dryer, so register is a moisture diffusion problem that depends on the paper’s history. A paper equilibrated at a different humidity registers differently on the same press. Register down a run with the web’s moisture logged would show the correlation.
Elastic memory
H5697. Repeat length on a web press is set by tension, but the web also carries the strain history of its unwinding and of the previous unit’s drying, so one tension gives different lengths before and after the dryer. The printed repeat records the web’s elastic memory rather than the tension setting. Repeat length measured at several points along the press at constant tension would show the memory.
Field-driven deposition
H5698. Ink misting on a high-speed press is attributed to the ink’s cohesion, but the fine droplets form charged at the film split and are then driven by the press’s electrostatic field, so the amount is a charging problem and the destination a field problem. A press with and without electrostatic assist, at one ink and one speed, would separate the two.
Stress rather than chemistry
H5699. An ultraviolet-cured ink that fails on a flexible substrate is reformulated for adhesion, but cure shrinks the film and puts the interface in tension, so a well-bonded film can still lift at a scratch. The failure is then a stress problem, and a more flexible ink treats it by lowering the modulus. Films of several moduli on one substrate, with stress measured by cantilever curvature, would show the lift threshold.
Self-bleaching depth limit
H5700. Through-cure of a pigmented ultraviolet ink is limited by the pigment’s absorption, but the photoinitiator is consumed and bleached as it works, so the depth that cures grows during the exposure and the front moves. A dose that fails to cure a thick film in one pass can cure it in two, because the first pass clears the path. Sectioning films cured in one and two passes, with hardness mapped through the thickness, would show the front.
Status and plan
One hundred entries, numbered in sequence. The subjects were chosen one at a time and the argument shape was chosen before the subject, so that no two entries rest on the same move; the label above each claim is there to be checked against the sentence beneath it rather than accepted as a taxonomy. Where a number appears it is an order-of-magnitude expectation offered as an estimate, not a measurement.
The scope is the colourant itself and the physics around it: the tautomer, the polymorph, the aggregate, the milled particle and its adsorbed layer, the photon that breaks a bond or a hydroperoxide, the pore that pulls the vehicle away from the pigment, and the nip that splits a film. Textile dyeing is a separate body of work and is not duplicated here.
If one of these is worth an experiment, it is H5616 — that the species absorbing the damaging photon is not the one that gives the dye its colour, but the minor tautomer whose absorption reaches further into the ultraviolet. It needs one dye, three solvents and a fade series read against the tautomer ratio.
Incoprea Research · hand-considered hypotheses 5601–5700 · 3 November 2026 · ~/Desktop/Nov3/