Permanence, Conservation, and the Long Life of a Painting

What Museums Know That Most Painters Don't

Why a watercolor's survival is determined before the first brushstroke — and what the conservation scientists who study the great masters have found inside their faded works

A Confession From the Tate

In the years following Turner's death in 1851, the British nation found itself in possession of something extraordinary and something alarming in equal measure. The extraordinary part was the bequest: nearly 300 oils, tens of thousands of works on paper, and sketchbooks numbering in the hundreds — the complete contents of Turner's studio, left to the country that had made him famous. The alarming part emerged gradually, as curators and conservators began to examine what they had inherited.

By the end of the 19th century it was becoming clear that watercolour pigments could easily fade over time. A struggle to conserve a collection of Turner's watercolours inherited by the Tate saw first hand the non-permanence of such pigments, prior to the specialist interventions we have today. This led to a slow decline in watercolour painting as a professional practice, due to a perceived loss of value and visual impact.

The pigments Turner had used with such freedom and brilliance across six decades were, in many cases, quietly destroying themselves. Many of the pigments Turner used, such as cochineal carmine and the chrome yellow shades, were known to fade in his lifetime. He used natural indigo, but this has faded dramatically, leaving behind grey or red skies where it was originally mixed with black or vermilion. Of course, along with light, the rate of fading in his paintings has been affected by factors such as humidity and atmospheric pollution. Turner preferred absorbent grounds and tended to keep his canvases in extremely damp conditions. This combination led to mould growth, discolouration, embrittlement, and flaking, which would have happened in his lifetime.

The Turner we see in the Clore Gallery today — magnificent and irreplaceable as it is — is not entirely the Turner he made. The grays that read as atmospheric mist were sometimes once vivid indigo. The pale sky passages that seem to vibrate with light were, in some works, originally painted in warm reds and oranges that have all but vanished. We are looking at survivals, not originals. And what survived is not a random selection — it is specifically the works made with the most durable materials in the most favorable storage conditions, while the more fragile passages have quietly receded toward invisible.

This is the essential fact that every painter, collector, and serious admirer of watercolor needs to understand. A painting's conservation history begins not in the conservator's studio but in the painter's decision about which pigments to use, which paper to use, and how to frame, store, and display the finished work. The choices made in the first hours of a painting's life determine whether it will survive its maker by a century or quietly disappear within a generation.

The Three Enemies

Everything that damages a watercolor on paper can be reduced to three agents: light, humidity, and acidity. They operate at different speeds and through different mechanisms, but they share a common feature: their damage is cumulative, progressive, and essentially irreversible. There is no conservation treatment that restores faded pigment to its original saturation. There is no chemical process that reliably un-yellows acidic paper to its original white. Prevention is everything.

The First Enemy: Light

Light is the most immediate and visible threat to watercolor, and the most counterintuitive one for collectors, who understandably want to display what they have acquired. Over even a small amount of time the ultraviolet light in sunlight can begin to fade the pigments and dry out the paper. Longer-term exposure may further embrittle the paper, either bleaching-out or turning an acidic paper an ugly yellowish hue.

The physics of light damage is straightforward. Photons of ultraviolet and high-energy visible light carry enough energy to break the chemical bonds within organic pigment molecules — the quinones, the azo groups, the phthalocyanine ring systems that give modern synthetic pigments their color. Once broken, these bonds do not reform. The color molecule is permanently altered, its light-absorbing properties changed. In many organic pigments this change manifests as fading; in others it manifests as darkening or color shift. The result in either case is a painting that no longer looks as its maker intended.

It is important to note that the lightfastness of a particular pigment can change depending upon the vehicle. For example, Vermilion (a vibrant red) has a lightfastness rating of I (Excellent) in oils and acrylics; however, in a watercolor vehicle it has a rating of III (not lightfast). For this reason, it is important to check the lightfastness rating for a specific manufacturer and medium whenever possible.

This point cannot be overstated. A pigment that is stable in oil — where it is surrounded and protected by the oil film — may be significantly less stable in watercolor, where it is bound only by a thin gum arabic film and directly exposed on an absorbent paper surface. The ASTM lightfastness ratings discussed in the pigment articles of this series are medium-specific: an ASTM I rating for watercolor means something different from an ASTM I rating for oil.

The measure of light damage is cumulative exposure — the product of light intensity and time. A painting hung in bright indirect light for ten years receives the same cumulative exposure as one hung in moderate light for twenty. Museums measure this in lux-hours — the unit of illuminance multiplied by time — and manage their display schedules accordingly, resting sensitive works in darkness between exhibition periods. The great watercolor collections at Tate Britain rotate precisely for this reason: the works are not all on permanent display because permanent display would destroy them.

For the private collector, the practical implications are clear. Watercolors should not be hung in direct sunlight under any circumstances. They should not be hung under fluorescent lighting, which emits ultraviolet radiation comparable in its damaging effect to diffuse daylight. It is advisable to hang a watercolor in a room with diffused incandescent or halogen light. Fluorescent lighting is as damaging as sunlight, producing ultraviolet light in high concentrations.

The single most important protective measure available — more important than any other framing decision — is UV-filtering glazing. UV glass, often referred to as UV-filtering or UV-protective glazing, is specially designed to block ultraviolet rays that cause fading and deterioration in artwork. Unlike standard glass, which offers little to no UV protection, UV glass can block up to 99% of harmful UV rays. The additional cost over standard picture frame glass is modest relative to the value of what is being protected, and the investment is permanent — the UV-filtering properties of quality conservation glass do not degrade significantly over decades.

The product landscape for conservation glazing has matured considerably. Tru Vue Conservation Clear offers excellent UV protection with minimal visual distortion. Museum Glass provides both UV protection and anti-glare properties, making it ideal for detailed work where surface reflections would distract from the image. For large or particularly valuable works, museum-quality glass is not a luxury — it is the minimum standard.

The Second Enemy: Humidity

Where light works on pigments, humidity works primarily on paper. Water vapor causes paper fibers to swell; dry conditions cause them to contract. The cycles of expansion and contraction produced by fluctuating humidity create mechanical stress in the paper substrate that, over years and decades, causes physical damage — cockle, warp, and eventually structural weakness in the cellulose fibers themselves.

Beyond the mechanical effects, humidity creates the chemical conditions in which biological damage occurs. Mold spores, present in virtually every indoor environment, require moisture to germinate. A watercolor stored in high humidity — above 65 percent relative humidity — is at significant risk of mold growth, which appears as the distinctive brown spots known as foxing. Foxing is not merely cosmetic: the fungal growth penetrates the paper fibers and, if unchecked, structurally degrades them.

For best results, maintain a temperature of around 70°F (21°C) and relative humidity between 40% and 50%. Using humidifiers or dehumidifiers can assist in keeping these levels stable.

The interaction between humidity and acidic paper is particularly damaging. Moisture accelerates the chemical reactions of acid hydrolysis that degrade cellulose — the same reactions that cause newspapers to yellow and crumble within decades. Acid paper in fluctuating humidity deteriorates measurably faster than the same paper in stable conditions.

There is an additional humidity threat specific to framed watercolors: moisture condensation on the inside of the glazing. When a cold exterior wall causes the glass to drop below the dew point of the interior air, moisture condenses on the glass surface — and if the paper is in direct contact with the glass, this moisture is transferred directly to the painting. It is most important that either a rag mat or fillets provide a space between the art and the glazing. Humidity can cause damage to the surface of the art if the paper is in direct contact with the glazing.

This is why matting is not merely aesthetic. The space created by a mat between the paper surface and the glazing is a conservation requirement, not a decorative choice.

The Third Enemy: Acidity

Paper acidity is the slowest of the three enemies — too slow for most collectors to perceive on any human timescale — and the most systemic in its effects. Acidic paper deteriorates from within: the hydrogen ions that define acidity attack the cellulose chains of which paper fibers are made, breaking them into shorter and shorter chains until the paper loses its structural integrity entirely and begins to fragment.

The sources of acidity in paper are multiple. Wood pulp paper is inherently acidic due to its lignin content. Atmospheric pollution — particularly sulfur dioxide from combustion — is absorbed by paper and converted to sulfuric acid. Acidic materials in contact with the paper — cardboard backing boards, wood pulp mats, certain adhesives — migrate their acidity into the paper over time. Even the paper itself can generate acid through oxidation.

The paper quality should be acid-free, as normal paper that is not acid-free will yellow and make the painting fade. If an acid-free paper is in contact with a NOT acid-free surface it will get affected and most likely start to fade after a few years. This can happen even if you are storing your artwork — keeping your artwork in an office paper folder or in a wooden draw, always be sure to keep the artwork in contact only with acid-free materials/surfaces.

The solution is systematic. Every material that contacts the paper — mat, backing board, tissue, adhesive, mounting hinge — must be acid-free and preferably alkaline-buffered. Alkaline-buffered materials contain calcium carbonate or magnesium carbonate that actively neutralize any acid that migrates from surrounding materials or the atmosphere. The additional cost over non-archival alternatives is negligible compared to the conservation value.

What Conservation Science Has Found Inside the Great Paintings

The development of non-destructive analytical techniques in the late 20th and early 21st centuries transformed what conservators can learn about historical watercolors without physically sampling them. X-ray fluorescence spectrometry, Raman spectroscopy, infrared reflectography, and multispectral imaging allow scientists to identify pigments, map their distribution across a painting, and detect changes that have occurred since the work was made — all without removing a single fiber from the paper.

What these techniques have revealed is simultaneously fascinating and sobering.

The Homer Revelations

Scientific evidence has shown that the sky in Winslow Homer's watercolor "For to be a Farmer's Boy" (1887) once glowed with color. In preparing for the Art Institute's major Homer exhibition, conservators discovered, using X-ray fluorescence spectrometry and visual examination through a microscope, that the painting's white skies were originally painted in unstable red and orange dyes that have almost completely faded.

Taking into account the pigment identification and nuances of shade and tone that are typical of Homer's paint handling, art conservators proposed a digital re-creation of the Homer watercolor. By shining laser light on particles buried in the artwork, SERS investigators have now unearthed the materials evidence that allows viewers to truly experience the hues of Homer's faded sunsets for the first time in modern times.

The Homer case is particularly instructive because the evidence connects directly to what was discovered at Bowdoin College: Homer's widespread use of red pigments based on cochineal is notable, and the effect of the fading of these colorants is discussed. The cochineal-based reds and carmines that Homer loved — vivid, warm, and intensely luminous — are among the most photosensitive of all historical watercolor pigments. Their fading is not gradual dimming but near-total disappearance, leaving the paper essentially blank where rich color once existed.

Color change in artworks has been commented on for centuries. Fading of watercolor pigments is a notable alteration. Pigments based on carminic acid are among those particularly prone to color loss. The research found that the comparative rate of fading is dependent not only on the pigment itself but on the pH of the paper substrate — acidic paper accelerating fading, alkaline paper showing different but sometimes equally problematic instabilities depending on the specific colorant.

This finding — that paper pH affects pigment stability — is one of the most practically important discoveries of modern watercolor conservation science. It means that even a well-chosen, theoretically lightfast pigment may perform below its rated stability on acidic paper. The pigment and the paper are not independent variables. Their interaction determines the actual longevity of the painted surface.

The Turner Science

The research of Dr. Joyce Townsend, senior conservation scientist at Tate and an expert on Turner and his materials, has revealed that his medium was mainly gum arabic — along with traces of gum tragacanth and varying levels of sugar or honey. Pigments found within Turner's watercolours include gamboge, quercitron yellow, vermilion, various iron oxides including ochres, umbers, and siennas, Indian yellow, green lake, Prussian blue, indigo, cobalt blue, blue verditer, and rose madder. He used watercolours in a block form and there is evidence he made some, if not all of them, himself.

Documents at Tate show that Turner closely followed pigment development and used new pigments as they appeared. This interest led him to use new pigments in favour of earlier ones with inferior or unsuitable properties. Turner also used Scheele's green (toxic copper arsenite), which he had substituted with emerald green by the 1830s.

Turner, in other words, was aware of the permanence problem — at least partially, and at least toward the end of his career. The substitution of Scheele's green suggests a painter who paid attention to new information about his materials and acted on it. But the broader record shows that he also continued to use gamboge, indigo, and rose madder — all of which have proven fugitive — throughout his career, apparently accepting their instability as the price of the specific visual qualities they offered.

This is the paradox that conservation science confronts in the historical record: the most beautiful colors were often the least stable. The vivid cochineal reds and carmines, the warm gamboge yellows, the luminous rose madder pinks — all of these contributed to the visual character that made 19th-century watercolor painting what it was, and all of them are now changed or gone in varying degrees from surviving works.

The Yale University Art Gallery has documented an equally revealing case. Conservators and conservation scientists studied a 16th-century Persian watercolor in which many of the skin tones had become darkened and discolored, as had the hillside. The XRF analysis revealed the presence of pigments such as vermilion, white and red lead, ultramarine blue, realgar, orpiment, verdigris, brown iron oxide, carbon black, gold, and silver. The darkening of lead white does not generally threaten the longevity or stability of the paint, but in many small artworks like this one, the original power and clarity of the figures and their expressions are often lost.

The Framing Decision: Where Most Damage Happens

The majority of preventable damage to privately owned watercolors occurs not through spectacular environmental events but through ordinary framing decisions made by people who did not understand the stakes. A watercolor framed with non-archival materials and hung in a moderately lit room will, within decades, show yellowing, foxing, or faded pigments — not catastrophically, not obviously at first, but cumulatively and irreversibly.

The components of archival framing, in order of importance:

Glazing

Standard glass and plexi/acrylic does not offer conservation — meaning that the piece is not protected from the damages caused by UV exposure. These damages include color fading, discoloration, and degradation. Once a piece of art or photograph is damaged by the effects of prolonged light exposure, there is really no turning back.

The glazing is the first line of defense and the highest-priority investment in a framing package. UV-filtering glass or acrylic that blocks 99 percent or more of ultraviolet radiation should be considered non-negotiable for any watercolor intended to last. Conservation Clear and Museum Glass from Tru Vue are the industry standards; there are increasingly competitive alternatives from other manufacturers that offer comparable UV protection at lower price points.

The choice between glass and UV acrylic involves a trade-off: glass is clearer and harder to scratch but heavier and breakable; UV acrylic is lighter, shatter-resistant, and often preferred for large formats, but develops surface scratches over time that can affect visual clarity.

Matting and Spacers

All materials in contact with the artwork must be acid-free and archival. This includes backing boards, mats, and hinges. These materials prevent yellowing, fading, and chemical breakdown that can occur when cheap materials are used.

The mat serves three functions: it creates a visual border that presents the work, it provides the air gap between paper and glazing that prevents condensation transfer, and it constitutes the most direct material contact with the paper's edge — which means it must be rigorously acid-free and alkaline-buffered.

Rag board mat — made from 100 percent cotton rag, the same fiber as quality watercolor paper — is the archival standard. It contains no lignin, no acid, and is typically buffered with calcium carbonate. Avoid wood pulp matboard regardless of its labeling: even "acid-free" wood pulp mats can off-gas acidic compounds over time.

Archival tissue paper is more appropriate for delicate media such as pastel, charcoal, soft graphite pencil, or opaque watercolor. Acid-free glassine is not recommended as it becomes acidic over time and easily distorts with fluctuations in humidity, potentially causing surface damage to the object.

This point catches many well-intentioned collectors: glassine interleaving, often used for storage, becomes acidic over time. Use acid-free tissue instead.

Mounting Hinges

The method by which the paper is attached to the mat or backing board matters considerably. The only archival mounting system for a valuable watercolor is a reversible one — one that can be undone with water or mild solvent without damaging the paper. Japanese tissue hinges attached with wheat starch paste or methylcellulose are the museum standard: they hold the paper securely, flex with humidity changes, and can be removed without trace by future conservators.

Pressure-sensitive adhesive tapes — masking tape, scotch tape, even many products marketed as "archival tape" — are not acceptable for mounting valuable works. Their adhesives yellow, migrate into the paper fibers, and become progressively harder to remove. The brown stains visible at the edges of many older watercolors in auction catalogs are almost invariably the residue of pressure-sensitive tape applied decades ago.

Backing Board and Sealing

The backing board — the material behind the paper inside the frame — should also be acid-free and alkaline-buffered. A layer of Coroplast (polypropylene) or foam-core (if acid-free) behind the rag mat board adds structural rigidity and a further barrier against moisture infiltration from the back.

The frame should be sealed at the back with acid-free tape to prevent dust, insects, and atmospheric pollutants from entering. Some framers add a sheet of MicroChamber paper — a product designed to absorb acidic gases — as an additional protective layer behind the backing board. In urban environments or areas with significant air pollution, this is a worthwhile precaution.

Storage: The Overlooked Category

Not every watercolor is framed and hung. Painters maintain flat files of unframed work; collectors acquire works that await framing; institutions hold far more in storage than they can display. The conditions in which unframed watercolors are stored determine their condition when they eventually emerge.

The principles are straightforward:

Interleave with acid-free tissue, not glassine, not standard paper. Each work should be individually wrapped or interleaved before storage.

Store flat, never rolled. Rolled storage is appropriate for some works on canvas but is damaging to watercolor paper, which can crack along the crease lines when unrolled after years.

Control temperature and humidity. The same parameters apply as for display: 68–70°F (20–21°C), 45–55 percent relative humidity. Avoid storage in attics (too hot, too dry in summer, too humid in winter), basements (consistently too humid, risk of flooding), or exterior walls (temperature fluctuations). An interior climate-controlled room is ideal.

Avoid wooden storage furniture for direct contact with the work. Wood off-gases acidic compounds that migrate into paper. Line wooden drawers and flat files with acid-free tissue or polyethylene sheeting before use.

Avoid plastic sleeves made from PVC (polyvinyl chloride), which off-gases acidic compounds. Use archival polyester (Mylar/Melinex) or polypropylene sleeves if clear storage is desired.

The Gum Arabic Question

A less-discussed conservation variable is the quality and quantity of the gum arabic binder in the paint itself. Gum arabic is a water-soluble polysaccharide — a complex sugar — that constitutes the binder in watercolor paint and determines how firmly the pigment is held to the paper surface.

Over time, gum arabic undergoes two types of degradation. It can dry and harden excessively, making the paint film brittle and prone to cracking or lifting if the paper is flexed. It can also cross-link in ways that alter its solubility — changing a watercolor's response to water in conservation treatment and making certain kinds of surface cleaning more difficult.

The sugar and honey additions that Turner used — documented by Dr. Joyce Townsend's research at Tate — were humectants, keeping the paint film flexible and rewettable. Similar humectants (glycerin, honey, ox gall) in modern commercial watercolors serve the same function and contribute positively to the long-term flexibility of the paint film. This is one reason why M. Graham's honey-based paints may have a slight conservation advantage in terms of paint film flexibility, though this has not been formally studied across the full range of aging conditions.

What is known is that excessively thick paint films — impasto-like applications in which the watercolor is applied at very high concentration — are more vulnerable to cracking and delamination than thin, well-diluted washes. The traditional watercolor approach of building value through multiple transparent layers rather than a single heavy application is not only aesthetically superior; it is structurally more stable.

The Long View: Making Work That Lasts

All of the foregoing converges on a set of practical decisions that every painter who cares about the long life of their work should make — not as afterthoughts, but as integral parts of the practice.

Choose permanent pigments. The ASTM I and ASTM II ratings from reputable manufacturers represent the most reliable lightfastness data available. Single-pigment paints from W&N, Daniel Smith, M. Graham, and Holbein rated ASTM I in watercolor provide the maximum available guarantee of stability. The beautiful but fugitive pigments of the historical tradition — genuine rose madder, gamboge, carmine, natural indigo — are available as historical curiosities, but using them in finished work intended to last is a choice made in full knowledge of the consequence.

Use 100 percent cotton rag, acid-free paper. As established in the paper article of this series, the fiber content of the paper is not a quality preference but an archival requirement. Wood pulp paper degrades from within regardless of how well the work is framed. Cotton rag paper, properly stored, will outlast any other variable in the painting's long-term survival.

Frame archivally and without delay. The practice of leaving finished watercolors in flat files indefinitely, awaiting framing, is a conservation risk. Unframed work is exposed to light fluctuations, handling damage, and atmospheric acidity in ways that framed work is not. A work worth making is worth protecting promptly.

Display consciously. Choose the wall. Avoid south-facing walls in direct sun, rooms with significant UV contribution from unfiltered windows, and locations near heat sources (fireplaces, radiators) that create localized humidity fluctuations. Rotate display periodically — even UV-filtered glass allows some visible light through, and cumulative visible-light exposure contributes to very long-term fading.

Store properly what is not displayed. The flat file is a conservation asset when used correctly. Interleaved with acid-free tissue, kept at stable temperature and humidity, away from exterior walls and direct light, unframed watercolors can survive for decades without significant degradation.

What We Owe the Work

There is a particular kind of grief that attends the conservation of historical paintings — the knowledge that what we see is already a diminished version of what was made, and that the diminishment is irreversible. The Homer sunsets that once glowed with cochineal red are now blank sky. The Turner indigo passages that once described a specific quality of evening light are now gray. The Persian miniature faces are darkened by chemical change rather than the artist's intention.

This grief has a productive form. It sharpens the responsibility that attaches to making work in the present — the recognition that the decisions made now will determine what future viewers find when they encounter the paintings that survive.

There are watercolors that are over 100 years old that are wonderfully fresh and crisp because they have been protected. With care, watercolors can last for posterity, and ensuing generations will appreciate the dedication to longevity.

Those crisp, fresh works — the Turner watercolors at Tate that were stored in darkness for decades between brief display periods, the Sargent watercolors at the MFA Boston and the Brooklyn Museum that have been kept behind UV glass in climate-controlled galleries — demonstrate what is possible when the full chain of conservation decisions is made correctly. They look, as closely as we can determine, like what their makers intended. The light in them is still the light the painter put there.

That is the goal. Not merely to make beautiful work, but to make work that remains beautiful — that carries forward, intact, whatever it was made to carry. The pigments, the paper, the framing, the storage, the display conditions: each one a link in a chain that either holds or fails.

The painter who understands this is not burdened by conservation anxiety. They are freed by it — freed to make the best possible decisions from the start, and then to paint with the confidence that what they create will be there, unchanged, when someone who has not yet been born stands in front of it a century from now.

That confidence is worth having. The work it enables is worth making.

Practical Summary: The Conservation Checklist

At the painting stage:

• Use single-pigment paints rated ASTM I in watercolor from reputable manufacturers
• Paint on 100% cotton rag, acid-free, pH-neutral paper (Arches, Fabriano Artistico, Saunders Waterford, or equivalent)
• Build value through transparent washes rather than heavy impasto application
• Sign and date in pencil or archival pigment ink on the back — never on the front in fugitive media

At the framing stage:

• Use UV-filtering glazing blocking 99%+ UV (Conservation Clear, Museum Glass, or equivalent)
• Use 100% rag mat board, alkaline-buffered
• Never allow the paper to touch the glazing directly — use mat or spacers
• Mount with Japanese tissue and wheat starch paste (reversible), never pressure-sensitive tape
• Use acid-free backing board and seal the frame back with acid-free tape

For display:

• Avoid direct sunlight and fluorescent lighting
• Keep ambient light levels moderate — dimmer is better for the painting even if dimmer for the room
• Maintain stable temperature (68–70°F / 20–21°C) and humidity (45–55% RH)
• Avoid exterior walls, above fireplaces, and near heating/cooling vents

For storage:

• Interleave with acid-free tissue, never glassine or standard paper
• Store flat, in acid-free boxes or portfolios
• Avoid wooden furniture contact without acid-free lining
• Avoid PVC sleeves; use Mylar/Melinex or polypropylene if clear storage needed
• Maintain same climate parameters as for display

Next and final in this series: Reading a Painting — how everything learned across this series changes the experience of standing in front of a watercolor in a museum, and what you will see that you could not see before.