Hand-considered hypotheses, 5501–5600
Written one at a time, not composed. This hundred stays inside art conservation and heritage science: pigment degradation, consolidants and coatings, environmental damage, dating, imaging of works, and the ageing of paper and canvas. Each entry carries its own logical-form label and no label is repeated, so the variety is structural rather than topical. None has been tested. No data are reported and no citation is made; where a magnitude is implied it is an estimate, marked as one.
Pigments: colour change and its mechanisms
Misattribution
H5501. Chrome yellow's darkening is blamed on the ultraviolet in daylight, but in the sulfate-rich orthorhombic form the rate-limiting step is water entering the lattice, so the darkening front follows the painting's humidity history more closely than its light dose. Two panels lit identically at different humidities should diverge, and the dry one should stay bright for decades longer — an estimate, since the hydration energy of the dispersed pigment is unknown.
Hidden term
H5502. Every measured rate of vermilion blackening contains a term proportional to the chloride available from the substrate, the ground, or the binder, and that term never appears in pigment-only light tests. One then expects the same pigment from the same maker to blacken at rates differing by an order of magnitude, estimated, when it is bound in a chloride-bearing glue ground rather than in oil.
Reaction front as clock
H5503. Blackening of lead white by hydrogen sulfide cannot penetrate deeper than the sulfide front, whose position is set by diffusion rather than by exposure time, so the depth of the dark layer is a clock and not a measure of damage. Cleaning a darkened lead white surface therefore exposes paint that has never reacted, which is why cleaned passages look younger than the passages beside them. Two paintings of equal exposure and different ground porosity should then show different front depths.
Inversion
H5504. Lead sulfide is re-oxidised to sulfate by light and oxygen, so a lead white that has blackened can bleach again, and a painting kept in the dark may end up darker than one that has been on display. A matched pair of darkened samples, one dark-stored and one dimly lit, should show an inversion of the usual dose-response.
Pathway identity
H5505. Pararealgar and arsenic trioxide, treated as two separate products of realgar's deterioration, may be one photo-oxidation pathway sampled at two oxygen activities. A single experiment sweeping oxygen concentration should then pass continuously from one product to the other without a change of mechanism, which would collapse two bodies of work into one.
Sub-threshold null
H5506. Prussian blue fading by reduction is balanced by re-oxidation, and below some light intensity the two rates could cancel so that no net fading occurs at all. The threshold would be set by the binder's oxygen permeability, which predicts that the same pigment under a low-permeability varnish has a higher threshold, and that a sample called light-fast may only have been tested dimly.
Degrees-of-freedom count
H5507. A visible reflectance curve of a mixture with N coloured components has at most N−1 independent shape parameters, so any unmixing that reports more pigments than that is fitting the instrument's noise. The check is a synthetic mixture of known composition, where the surplus components should still appear even though they are absent. The surplus is usually small, which is exactly why it is mistaken for precision.
Particle-size invariance
H5508. Potassium leaching from smalt is diffusion-limited inside each particle, and above a particle radius of a few micrometres, an estimate, the decolorisation per unit area becomes independent of size. Grinding smalt finer should therefore not accelerate its greying, contrary to the workshop belief that the fine grade is the unstable one.
Phase degeneracy
H5509. Azurite that has converted to malachite and malachite that was painted as such are indistinguishable by phase identification of a microsample, and only the pseudomorphic texture separates them. Any provenance argument resting on malachite's presence in a blue passage is therefore degenerate until the texture has been examined. Under the microscope a replacement keeps the original crystal's outline, while a painted malachite does not.
Bistability
H5510. Copper resinate occupies two colour states, green and brown, at the same overall composition, depending on whether the copper is held as a carboxylate or has segregated as oxide, and the switch between them is cooperative. Colour is then not a monotonic function of age, and a brown passage can be chemically younger than the green one beside it.
Conserved quantity
H5511. Arsenic is conserved during orpiment deterioration and only its location changes. Measuring the arsenic in the layers adjacent to an orpiment particle, rather than the arsenic left inside it, turns a vague report of degradation into a mass balance that can be closed. The measurement needs a drill core and an elemental map, not a bulk assay of the particle.
Dark control
H5512. If cadmium yellow whitening is photocorrosion to cadmium sulfate, a sample kept in the dark at the same humidity must not whiten, and if it whitens then humidity alone is sufficient and light is merely accelerating a reaction that needs no photons. The control is cheap and appears rarely to have been run. The result is binary, which is why it is worth doing before any spectroscopy.
Order of limits
H5513. Whether a zinc white oil film embrittles or saponifies depends on which of two diffusing species arrives first, oxygen or water, and the two limits predict opposite behaviour for thick and for thin films. A thin-film study therefore cannot be extrapolated to a painting, because the film's thickness selects which limit applies.
Reciprocity failure
H5514. Photodegradation of organic lakes is mediated by singlet oxygen whose steady-state concentration rises sublinearly with intensity, so damage per unit exposure is greater at low light than at high. Lighting limits set from bright accelerated tests therefore understate the damage of a long dim exhibition, and the correction is largest for the most sensitive lakes. The size of the effect follows from the termination kinetics alone, without knowing which lake is involved.
Autocatalysis
H5515. Iron gall ink corrosion accelerates because the first oxidation liberates more soluble iron, which catalyses further oxidation, so the ink shows an induction period followed by a steep rise. The induction time, not the final iron content, is the quantity that should decide treatment.
Inhibition by coating
H5516. Titanium white's photocatalytic activity is suppressed by the alumina and silica coating on each particle, and that suppression is lost when the coating is abraded during dispersion. The binder's lifetime is then set by the dispersion's energy rather than by the pigment's grade, which would explain why two paints of identical specification age differently.
Surface reservoir saturation
H5517. Indigo fading saturates because once the indigo at the air interface is consumed, the remaining pigment lies behind a binder layer that absorbs the actinic wavelengths. A fading rate measured on a long-exposed sample is therefore an underestimate of the initial rate, and accelerated tests should report the early slope. The early slope is the only part of the curve that reports the material rather than the lighting.
Connectivity threshold
H5518. Salt damage in a porous paint begins at the salt content where the pore network first becomes connected, not at a critical concentration in the bulk. Two paints with the same salt loading can then differ entirely, one efflorescing and one remaining sound, according to their pore connectivity.
Interfacial passivation
H5519. Verdigris darkening is controlled at the pigment-binder interface, where a coherent copper carboxylate layer forms and slows further reaction, rather than in the pigment's interior. Darkening should therefore stop at a conversion depth of a few nanometres, an estimate, however long the paint is exposed.
Sampling artefact
H5520. A cross-section samples depth in proportion to each layer's thickness, and degradation is concentrated near the surface, so any kinetics derived from a section is a depth-weighted average that depends on how the section was cut. Two laboratories cutting at different angles should report different rates from the same painting.
Survivorship bias
H5521. The pigments called stable are the ones that survived, so stability rankings drawn from collections have the wrong denominator. The correction is to compare survival against production volume rather than against surviving works, which would demote several pigments currently regarded as permanent. Production records, not collection catalogues, are the missing half of the comparison.
Confounder
H5522. Smalt's blue loss measured in oil is confounded by the oil's own yellowing, because both track the painting's storage history and the yellowing mimics the loss in reflectance. The confound can be broken only by a measurement blind to the binder, such as the cobalt's absorption in the near infrared.
Proxy nonlinearity
H5523. Reflectance is used as a proxy for chromophore loss as though the relation were linear, but at high loss the remaining colour is dominated by scattering and the proxy saturates. Fading curves from strongly faded passages are therefore compressed, and the true loss is larger than the proxy reports.
Coincidence of timescales
H5524. The correlation between lead white's darkening and a painting's age may be a coincidence, with sulfide formation and oil yellowing running on similar timescales without sharing a cause. Separating them needs a pigment that does not sulfurise, against which the oil's contribution can be measured. A non-sulfurising pigment is not hard to find, only rarely included in the test set.
Impossibility of attribution
H5525. When light and a pollutant produce the same product, the final state cannot say which did it. The distinction has to come from a spatial pattern, since light is directional and pollution is not, and a hypothesis that ignores the pattern is untestable.
Binders, varnishes, and consolidants
Hidden variable
H5526. Linseed oil's yellowing is treated as one process, but it carries a term from the driers used at the time, and lead or manganese driers yellow differently from cobalt ones. Two oils of identical age can therefore differ visibly, and a reconstruction without the historical drier will not reproduce the original's colour.
Reversal of selectivity
H5527. A solvent that swells a varnish also swells the paint beneath it, and the ratio of the two swellings passes through unity at a particular solubility parameter, so the selectivity reverses across a narrow window. Cleaning formulations chosen on the varnish's solubility alone can sit on the wrong side of that reversal. The window is narrow enough that a few percent of one solvent in another can cross it.
Percolation of consolidation
H5528. Below a critical concentration a consolidant does not form a continuous bridge network between particles, and it adds colour without adding strength. That threshold is a percolation property of the pore filling and depends on the stone's porosity rather than on the polymer's concentration in the bottle.
Identity of two symptoms
H5529. Whitening at a consolidated surface and hazing within it may be the same phase separation of polymer from residual solvent, seen at different length scales. Treating them as distinct faults has produced two sets of remedies for one problem.
Transport latency
H5530. Nanolime appears inert for weeks and then hardens, because carbonation waits on carbon dioxide diffusing into the pore. The delay is a transport time and should scale with the square of the penetration depth, which makes it longer in dense stone even when the chemistry is identical.
Race between rates
H5531. In an acrylic consolidant, solvent evaporation and chain entanglement compete, and if evaporation wins the film stays weak and re-soluble. Application thickness decides which wins, so the same product can give a durable or a friable consolidation depending on how it was brushed. Thin applications therefore cure better than thick ones, the opposite of the instinct to load the brush.
History dependence
H5532. A paint film's modulus depends on the highest humidity it has previously experienced rather than on its present humidity, because physical ageing erases the memory of lower values only slowly. Two films equilibrated at one humidity can then differ, and a conditioning protocol can erase the very history it means to study.
Mass-budget closure
H5533. The consolidant that matters is the fraction that stayed where it was placed, while surface uptake measurements count the fraction that wicked away as success. Closing the mass budget requires weighing the interior, which is destructive, so most reported efficiencies are upper bounds. Quoting the wicking ratio beside the uptake would make two studies comparable that now are not.
Sufficiency failure
H5534. Knowing a varnish's glass transition temperature does not predict whether it will crack, because cracking depends on the stress at the temperature of use and on the substrate's restraint. A low-transition varnish can survive where a high-transition one fails, so the single number is not sufficient and its use as a criterion should be abandoned.
Necessary condition
H5535. A consolidant can work only if its drying shrinkage is accommodated by the pore's elasticity, and where shrinkage exceeds that accommodation the treatment must fail whatever the polymer's chemistry. That condition is evaluable before treatment, and it rules out most of the documented failures in advance.
Non-identifiability
H5536. Indentation of a consolidated surface yields one curve, and the stiffness and thickness of the consolidated layer trade off against each other in fitting it. The two cannot be separated without an independent measurement of mass uptake, so reported consolidation depths are usually a choice of fit rather than an observation.
Error dominance
H5537. In tensile testing of a painted canvas the reported scatter in Young's modulus is dominated by the extensometer's own compliance, not by the material. The check is to test the same strip at two attachment lengths, which should shift the apparent modulus systematically if compliance is the cause.
Counterfactual claim
H5538. A treatment is reversible only if the solvent can reach the interface it must undo, and in a porous substrate the diffusion path can be longer than the interval between treatments. Reversibility is thus a claim about plumbing rather than about chemistry, and it should be stated together with the path length that makes it true. The path length is measurable by tracer penetration, and it belongs in the treatment record.
Cross-contamination
H5539. Solvent gels leave residues below the detection limit but not below the threshold of chemical activity, and those residues alter the next treatment's penetration. The effect is a hidden term in every later measurement, and it can be exposed by treating a blank with the gel and measuring what it does to a fresh film.
Square-law scaling
H5540. Solvent penetration into a varnish is diffusive, so the working time before the solvent reaches the paint scales with the varnish thickness squared. Thick varnishes are therefore not merely slower to remove but qualitatively harder to remove cleanly, which explains failures blamed on the solvent.
Free-volume argument
H5541. Residual solvent in a dried acrylic film occupies free volume and leaves slowly, changing the film's refractive index and therefore its appearance for months. Drying and appearance stabilisation are different events, and a treatment judged satisfactory when touch-dry may still change colour for a season. The index change is small, but it is systematic and runs in one direction only.
Catalytic trace
H5542. Residual iron in an earth pigment catalyses the crosslinking of the oil around it, so the binder's cure is accelerated locally and the paint's age is not the painting's age. A measurable gradient in crosslink density away from iron-rich particles would date the cure rather than the work.
False correspondence
H5543. Gloss and oxidation are two variables that correlate only because both follow exposure, so treating one as a measure of the other fails whenever exposure is uneven. A varnish can be glossy and heavily oxidised if it was polished, and gloss cannot substitute for a chemical measure of oxidation.
Underdetermined inverse
H5544. Many varnish histories produce the same gloss and colour, so recovering a history from appearance is underdetermined. Cleaning decisions framed as restoring the original therefore amount to choosing among equally consistent histories, and the choice should be argued on grounds other than the measurement.
Masking
H5545. A yellowed varnish masks the yellowing of the oil beneath it, so removing the varnish reveals a colour change that is then attributed to the cleaning. The change predates the treatment, and the misattribution persists because the before-and-after comparison has no independent measure of the oil. A cross-section taken before and after cleaning would settle the attribution without argument.
Environmental recurrence
H5546. A consolidant stable for decades can fail within a season when the humidity crosses the value that plasticises it, so the failure is a threshold in the environment rather than in the material's age. Monitoring the humidity across that value matters more than monitoring the treatment's age.
Selection effect
H5547. Consolidants are judged by the treatments still visible, since the failures were re-treated and dropped from the record, and the reported success rate therefore has no denominator. A registry that includes the re-treated cases would be worth more than any further laboratory comparison. The missing number cannot be recovered retrospectively, only prospectively.
Inverse-size scaling
H5548. The shrinkage stress a drying consolidant exerts on a particle scales inversely with the particle's radius, so a formulation safe on coarse pigments will crack fine ones. This explains the common pattern in which whites survive a treatment that destroys lakes, and it predicts which passages to test first.
Absorption-length limit
H5549. A protective coating stops helping once its thickness exceeds the absorption length of the damaging wavelength, and beyond that thickness it adds only a moisture barrier and a refractive interface. The optimum is therefore a definite thickness, and the belief that more coating is safer is wrong on both sides of it.
Thermodynamic limit
H5550. The lowest humidity achievable in a sealed case is set by the strongest hygroscopic material inside it, not by the mass of silica gel, so adding gel to a case containing a hygroscopic object cannot go below that floor. The floor belongs to the contents and is approached asymptotically, which is why some cases stall at a humidity no amount of gel will lower.
Paper and canvas
Misattributed persistence
H5551. Paper yellowing is attributed to light, but in lignin-containing stock the yellowing continues in the dark from peroxides left by manufacture, and the dark rate can exceed the lit rate in the first years. A dark-stored control is the whole experiment, and it is rarely reported.
Measurement-medium artefact
H5552. The pH of unbuffered paper measured with a water drop includes the carbon dioxide the drop absorbs while equilibrating, so the reading drifts toward the water's own pH and not the paper's. The artefact is largest for papers closest to neutral, which are exactly the ones whose treatment depends on the number. Measuring in a closed cell with the carbon dioxide stripped would show whose drift it is.
Life bound
H5553. A paper's service life is bounded by the number of chain scissions it can accumulate before strength is lost, not by its pH, and two papers at the same pH can differ by decades, an estimate, in that budget. Reporting pH as a durability index conflates a rate with a capacity.
Inversion of a treatment
H5554. Deacidification can accelerate the degradation of an already oxidised paper, because alkaline conditions promote the elimination reactions that the oxidised groups have primed. The treatment that protects a fresh paper can therefore destroy an aged one, and the decision should turn on the carbonyl content rather than on the pH.
Critical moisture content
H5555. Hydrolysis stops below a moisture content at which the reactants can no longer meet, so a dry state is protective only below that value and not at any humidity a room might reach. What matters is the fibre's bound water rather than the air, which is why silica gel can work where a dry room does not.
Mechanistic identity
H5556. Foxing spots and iron-gall corrosion may be the same iron-driven oxidative process at different iron concentrations, with the distinction quantitative rather than mechanistic. If so, the foxed sheet and the ink-corroded sheet should respond to the same chelating treatment, which is a cheap test of the identity claim. If the identity holds, one protocol serves both sheets and the separate treatments are redundant.
Count
H5557. The fibre species that can be independently identified in a sheet are limited by the number of orthogonal optical contrasts the microscope provides, so a report of five species from bright-field alone is at least partly an artefact of orientation. Counting species from a single micrograph therefore overstates the furnish's complexity.
Optical artefact
H5558. Apparent brightening after aqueous treatment is often an artefact of measuring a wetted sheet against a dry reference, since water changes the refractive index match between fibres and air. The paper has not changed and the geometry of the measurement has, so a re-measurement after full equilibration should remove the effect.
Percolation of strength
H5559. The strength of aged canvas does not fall in proportion to its degree of polymerisation; it holds up and then collapses at a critical value, because load paths must percolate through intact chains. The collapse is the threshold that matters, and the gradual loss before it is nearly invisible mechanically.
Hysteresis
H5560. Canvas dimensions depend on the humidity history and not on the current humidity, because wetting swells the fibres more than drying recovers. Two canvases can therefore stand under different tensions at the same recorded humidity, and a survey that records only the present humidity misses the variable that governs the strain.
Anisotropy
H5561. Cracks in a painting follow the weave's anisotropy, so their direction records the loom rather than the painting's handling. Reading crack patterns as evidence of transport or of rolling is therefore unsafe unless the weave's orientation is known independently. Weave orientation is recoverable from raking light, so the check costs nothing.
Residual-stress memory
H5562. The tenting of canvas at a stretcher bar is a residual stress field from the original stretching, frozen in by the ground, and it persists long after the tension is gone. Its geometry can be inverted to recover the original stretching pattern, which makes the deformation a document rather than a defect.
Scattering-limited depth
H5563. Ultraviolet light penetrates paper only to a depth set by the fibres' scattering, so photodegradation is confined to a surface layer while the bulk remains intact. Surface yellowing therefore overstates the sheet's overall damage, and any dating method assuming uniform oxidation will misdate thick sheets. The depth can be estimated from the sheet's opacity, which is measured anyway.
Coupled ageing
H5564. Hydrolysis shortens the cellulose chains and the shorter chains plasticise the fibre, so a canvas can become weaker and more extensible at the same time. The two changes are coupled, and measuring one while assuming the other constant inverts the interpretation of the other.
Impossibility of separation
H5565. Chemical and mechanical strength loss reduce the same measurable, so the canvas alone cannot say which dominated. Only the fibre's fracture surface distinguishes them, which means the diagnosis needs a destructive sample and cannot be made from tensile data.
Superposition failure
H5566. Time-temperature superposition fails for paper because hydrolysis and oxidation have different activation energies, so a single acceleration factor cannot map a warm test onto a cool store. The error is not random but changes sign as the mechanism changes, which makes an accelerated life prediction wrong in a direction that depends on the test temperature.
Compensation effect
H5567. In paper ageing the apparent activation energy and the pre-exponential factor move together, so extrapolations from several temperatures converge on a spurious isokinetic temperature and appear consistent. The consistency is an artefact of the compensation, and a wider temperature range is the only way to expose it.
Endpoint selection
H5568. An ageing test that scores a fixed drop in degree of polymerisation selects for the fastest mechanism at the test temperature, which may not be the mechanism that dominates at room temperature. The test therefore ranks materials by a mechanism that the store may never exercise. The whole curve, not the endpoint, would remove the selection at no cost.
Gatekeeper variable
H5569. Whether a canvas's degradation products escape depends on the ground's pore structure rather than on its chemistry, so a tight ground traps the acids it was meant to keep out. The ground's permeability is the gatekeeper, and measuring it should precede any choice of lining adhesive.
Protective impurity
H5570. Linen's natural waxes and pectins slow hydrolysis at the fibre surface, so a scoured and bleached canvas can be less stable than a raw one. Purity is not the same as permanence, and the conservation grade that removes the impurities may remove the protection with them.
Coincidental correlation
H5571. Thread count correlates with painting date only because the textile trade's economics changed, so dating a canvas from its weave assumes the trade's history and then claims to recover it. The correlation is real but circular, and it should not be used where the trade's local history is unknown. A documented local trade turns the assumption into a measurement.
Compliance bound
H5572. The number of times a canvas can be lined is bounded by the accumulated adhesive layers' compliance rather than by the canvas's strength, so every lining spends an irreversible part of a fixed budget. That budget is the quantity to record, and it is recorded nowhere.
Environment, pollution, and climate
Deliquescence point
H5573. Salt damage begins at the humidity at which the salt mixture present deliquesces, and below that humidity cycling does no harm however many cycles occur. The controlling number is the mixture's deliquescence point and not the individual salts' points, so a minor component can set the damage threshold for the whole.
Dose composition error
H5574. The sulfur dioxide dose delivered to a stone includes the deposition velocity's dependence on surface wetness, so a dose computed from concentration and time is largely a wetness term in disguise. Two sites at the same concentration can differ severalfold in dose, an estimate, according to how often their surfaces are wet. Wetness is rarely logged, which is why the discrepancy is rarely noticed.
Sign inversion under buffering
H5575. Ventilating a display case can be worse than sealing it for a hygroscopic object, because ventilation imports moisture during the humid part of the day and exports it during the dry part, amplifying the cycle the object sees. The sign of the effect depends on the object's buffering, so one case design is right for a metal and wrong for a panel.
Conserved water budget
H5576. The water in a microclimate is conserved, so a frame's buffering capacity is a property of the enclosed materials' total sorption and not of the frame's seal. Adding a desiccant to a well-sealed frame therefore does less than expected unless its mass is compared with the wood's. The comparison is arithmetic and can be made from a small sample of the wood.
Amplitude bound
H5577. The humidity amplitude inside a case cannot exceed the outside amplitude multiplied by the ratio of the driving period to the case's diffusion time constant, so a stable case is one with a long time constant rather than a tight seal. The bound can be estimated from leakage and volume before anything is built.
Competing annealing
H5578. Light generates radicals in a varnish while moisture anneals them, so yellowing should be greatest at intermediate humidities and fall at both extremes. A maximum in the damage-versus-humidity curve would explain why some well-ventilated stores show less yellowing than expected.
Sink saturation
H5579. Reciprocity between pollutant concentration and exposure time holds only while the surface is a perfect sink, and at low concentrations the surface saturates so that the product of the two overstates the damage. The saturation belongs to the reaction sites, and it makes a long low-level exposure less damaging than a short high-level one of the same product.
Limit crossover
H5580. A gypsum crust on stone may protect the stone or destroy it, according to which dominates, the crust's diffusion resistance or its content of soluble salt, and the outcome is opposite in the two regimes for a crust of identical thickness. The crossover thickness is measurable and should decide whether a crust is removed or left.
Shelter confounder
H5581. The appearance of outdoor bronze is confounded by shelter geometry, since sheltered surfaces accumulate chlorides that exposed ones wash off, so a colour map is largely an exposure map. Attributing colour to pollution without recording the shelter attributes it to the wrong variable.
Positive feedback
H5582. Biological growth on stone retains water, which favours further growth, so the clean state is unstable and the colonised state reinforces itself. This makes the timing of cleaning more important than the choice of biocide, because a partial cleaning can return the surface to the unstable state with a larger inoculation.
Network latency
H5583. Thermal shock damage in a ceramic appears only after many cycles, because the microcrack network must become connected before it can accommodate the strain. The latency is a network property, so one cycle at a severe amplitude can do less harm than many at a mild one.
Selective penetration
H5584. Ozone attacks the surface of rubber but the bulk of paper, because the materials differ in how fast the oxidant is consumed relative to how fast it diffuses. A single oxidant dose therefore cannot rank materials, and the ranking reverses with thickness. The reversal follows from the ratio of reaction rate to diffusion coefficient, and it should be predictable.
Self-pollution crossover
H5585. Below a minimum air exchange rate, pollutants emitted by the objects themselves accumulate faster than ventilation removes them, so a sealed case can end up dirtier than one with a small leak. The crossover rate is set by the object's emission and the case's volume, and it is the number case design should meet.
Non-attributable integral
H5586. Damage is an integral over the exposure history, so a single environmental record cannot attribute it to a specific excursion unless the record also carries the object's response time. Without that time constant the attribution is a narrative rather than an inference. Step changes in the record are therefore the only features that can be tied to an event.
Imaging and instrumental analysis
Thickness-composition degeneracy
H5587. A thin layer of lead white and a thicker layer of a lighter pigment attenuate X-rays identically, so a radiograph's apparent density is a degenerate mixture of thickness and composition. Reading a radiograph as though it showed the support alone is an assumption rather than an observation.
Projection ambiguity
H5588. Macro-XRF element maps are projections through the whole stratigraphy, so a signal from a hidden layer and one from the surface are the same measurement. A hidden pigment can be claimed only where a depth-selective method confirms it, and maps that ignore this show sum totals rather than layers.
Contrast-mechanism error
H5589. Infrared reflectography's contrast comes from the paint's transparency and not from the underdrawing's material, so a carbon underdrawing beneath a carbon-free paint is invisible while a non-carbon drawing beneath a carbon paint may show. An absence of underdrawing in an infrared image therefore means an absence of contrast, which is a statement about the paint and not about the artist.
Spot-size bound
H5590. The resolution of a scanning image is bounded by the source's spot size rather than by the pixel count, so oversampling adds file size and no information. A knife-edge target scanned at two pixel pitches should show the same edge width if the spot is the limit.
Interface artefact
H5591. An optical coherence tomogram's apparent varnish layer can be a refractive-index interface within the paint, so layer counts overstate the varnish and understate the paint. The ambiguity is resolved only by an independent thickness measurement at the same point, which is rarely made. A second angle of incidence would separate the two, since only one of them moves with it.
Point-sampling bias
H5592. A Raman spectrum from one point on a heterogeneous paint is a random draw from a skewed distribution, so a single identification is not the passage's composition. Reporting the number of points and their positions matters as much as the identification itself.
Fluorescence masking
H5593. The fluorescence background of a degraded varnish hides the Raman bands that would date it, so the measurement's failure is read as the material's absence. Shifting the excitation wavelength is the obvious remedy, and its absence from most reports suggests the failure is being misread. The shift costs one laser line and one filter, which is little against a wrong conclusion.
Bandwidth-penetration trade-off
H5594. Terahertz imaging's depth resolution is set by the pulse's bandwidth, and higher frequencies give finer layers with shallower penetration, so the trade-off cannot be optimised away. The choice of band is therefore a choice of which layer to see, and one image cannot answer both questions.
Redundant readout
H5595. Ultraviolet fluorescence and visible colour of a varnish are two readouts of the same oxidation variable, so agreement between them is not independent confirmation. Treating them as two lines of evidence doubles the apparent certainty without adding information.
Detection limit
H5596. A pigment is detectable by X-ray fluorescence only above an areal density that depends on the layers above it, so a missing line in a spectrum means below that limit and not unused. The limit moves with the overpainting, which makes an absence in a heavily overpainted area the least informative result in a survey.
Proxy circularity
H5597. Craquelure density is used as an age proxy, but the density is set by the ground's mechanics and the panel's restraint, so it dates the preparation rather than the picture. Using it to order works by date assumes the chronology it claims to establish. Independent dendrochronology from the panel would break the circle, where the panel survives.
Mixture non-identifiability
H5598. A mixture of two pigments and a single pigment with a surface coating can produce the same reflectance spectrum, so spectral unmixing is underdetermined without a constraint from another modality. The constraint is usually assumed rather than measured, which is where confident attributions come from.
Library bound
H5599. Hyperspectral identification of a pigment is bounded by the completeness of the reference library rather than by the instrument's resolution, so a finer spectrometer does not by itself improve accuracy. The binding constraint is the library's coverage of the materials actually used, which is a curatorial problem rather than an optical one. Improving the library is unglamorous, which is why it lags the instruments.
Null discriminator
H5600. If a reported subsurface signature is real, it must survive when the illumination moves to a wavelength at which the overlying pigment is transparent, and if it vanishes the signature belongs to the surface. Such a null test costs one filter change and would settle several published claims.
Status
100 entries, H5501–H5600. The forms are uneven in weight on purpose: some entries are bounds, some are degeneracy claims, some are inversions of a treatment habit, and a few are worth writing down only because they can be falsified with equipment already in the studio.
If one of these is worth an experiment, it is H5512 — that a cadmium yellow which whitens in the dark has been misdiagnosed as a light problem all along. It needs two samples, one drawer, and a month.
Incoprea Research · hand-considered hypotheses 5501–5600 · 3 November 2026 · ~/Desktop/Nov3/