Choosing a consolidant in restoration doesn't start by comparing products: it starts by deciding if consolidation is even necessary. This guide goes beyond manufacturer datasheets and conservation literature, and it's written to help you approach a product sheet already knowing what you're looking for.
We haven't seen your artwork, and that affects everything that follows: each piece has its own material history, and what works on a polychrome on wood might be exactly what you shouldn't use on paper. Everything you read here should first be tested in an inconspicuous area.
Consolidation is not the first step in an intervention. It is a decision. A consolidant applied to a layer that didn't need it cannot be removed afterwards: it remains embedded.
The short answer, if you came looking for which one to choose: the consolidant is determined by the problem, not the catalog. First, you find out what caused the degradation, because if the cause is still active, consolidating it fixes it in place. Then you distinguish whether the layer is powdery or lifted, as these require different materials. Next, you check what solvent the artwork tolerates, which rules out entire families. And only then do you choose the product and concentration, always starting with the lowest.
Disaggregation or disadhesion? They are not the same problem
They are constantly confused and require different responses.
Disaggregation is the loss of cohesion within the same stratum. The material has lost its ability to hold itself together: a powdery paint layer that rubs off with the touch of a finger, a preparation that disintegrates, stone that turns to sand. The material remains in place, but it falls apart.
Disadhesion is the loss of adhesion between strata. The layer is intact but has detached from what lies beneath it: lifted flakes, cupping, blistering. Here the material does not fall apart, it separates.
How to distinguish them, with what you have on hand:
- Raking light. Placed almost parallel to the surface, it reveals relief: liftings cast shadows, powdery areas do not.
- Observation under magnification. A linen tester loupe or a binocular magnifier is sufficient to see if the edge of the lesion is lifted or disaggregated.
- An inconspicuous area, always first. The reverse, an edge under the frame, a corner that isn't visible.
The answer changes completely: a powdery layer requires a consolidant that penetrates and restores cohesion; a lifted flake requires an adhesive to reattach it, applied from underneath. Confusing them leads to saturating a surface with product that only needed to be re-adhered.
The five questions before choosing a consolidant
1. What has degraded, and why?
A consolidant does not fix the cause. If the polychromy is lifting because the support moves with changes in humidity, consolidating without addressing the movement is postponing the problem and adding a new material to the equation.
2. What is compatible with the original artwork?
Compatibility takes precedence over performance. A protein binder, a chalk ground, and an oil layer respond differently to water, heat, and solvents.
3. What solvent does the artwork tolerate?
This question rules out entire families before looking at any product. If the artwork is sensitive to water, cellulose ethers in an aqueous medium are out.
4. What reversibility do you truly need?
Reversibility is not an absolute property, and it's advisable to be wary of the word when it appears alone. A material can be reversible the day it is applied and not twenty years later.
5. What does its manufacturer declare it for?
This is the question almost no one asks, and the one that resolves a doubt most quickly.
What a manufacturer declares for its product depends on who they manufacture it for. A company that formulates for conservation states on its datasheet what it's for in conservation. A chemical company whose material reaches the sector repackaged documents the use for its market, which is usually different: pharmacy, construction, chemical industry.
Neither of these things makes a material suitable or unsuitable. What changes is where the backing is: in the manufacturer's datasheet, or in the Conservation-Restoration (C&R) literature that has studied that use. Checking this before buying is part of the job, and it's done by opening the technical datasheet of the manufacturer.
The consolidant families, and what each one solves
There is no order of quality here. There are materials that solve different problems. All those mentioned are in the collection of adhesives and consolidants.
Cellulose ethers
Cellulose derivatives soluble in cold water. They are used in paper works, sensitive polychromy, and as light fixatives, and share a chemical nature with cellulosic supports.
In the catalog, Klucel® G (hydroxypropylcellulose) and Tylose MH 300 P2 (methylhydroxyethylcellulose).
Three things to know before using them, which may be surprising:
- They dissolve in cold and become insoluble when hot. It's the opposite of what one expects. Kremer's datasheet for Klucel G states it as insoluble above 45 °C. Heating the water doesn't help: above that point, the polymer stops dissolving.
- Aging can reduce their solubility. Feller and Wilt, in their study of cellulose ethers for the Getty Conservation Institute, documented a loss of solubility after thermal aging. "Reversible" accurately describes the freshly applied film; it's not a thirty-year promise.
- Water is not their only solvent. Klucel G is also soluble in ethanol and other polar solvents, according to its manufacturer. This is exactly what's needed when the artwork cannot tolerate water.
Regarding the prepared solution, Ashland warns that it is sensitive to acid hydrolysis and recommends buffering it between pH 6.0 and 8.0. This is an indication about the liquid you prepare, not about the film once dry.
Concentration and application: start low and repeat. The working concentration comes from the datasheet of the product you have, not from a general recipe.
Polysaccharides and protein glues
Naturally sourced materials, with a long tradition of use and very different behaviors among themselves.
JunFunori® Glas is a polysaccharide purified from red algae. Lascaux declares it for the consolidation of matte and powdery paint layers, which is exactly the case of disaggregation described above.
Also in the catalog are sturgeon glue, rabbit skin glue and wheat starch.
Concentration and application: these are materials that are prepared, not bought ready-made. The working concentration comes from the datasheet of that specific product, not from a general recipe.
Acrylic resins in aqueous dispersion
They arrive dispersed in water and form a film upon evaporation.
Lascaux Medium for Consolidation is an acrylic dispersion that its manufacturer literally declares "for the consolidation of paintlayers in medieval polychromy on wood". It is worth reading that full phrase: it talks about medieval polychromy on wood, and Lascaux's reference substrate is chalk ground. Outside of this assumption, it is still a conservation material, but the manufacturer is no longer speaking directly to that use.
Acrylic resins in solvent
Paraloid B-72 is an acrylic copolymer that has been used in conservation since the 1950s, both for consolidating and varnishing. Lascaux, in its technical datasheet, lists it for consolidating and impregnating murals and oil paintings, as a fixative for charcoal, chalk, and pastel drawings, and for wood consolidation.
Concentration and application: the manufacturer itself recommends working with low concentrations and repeating the application if necessary, and warns of the risk of saturation when over-concentrating. Its uses and preparation are detailed in the Paraloid B-72 guide.
Polyoxazolines
Aquazol® 200 is a poly(2-ethyl-2-oxazoline), soluble in both water and alcohols, which expands preparation options.
And it has a specific condition that determines if it's your material or not. In a humidity chamber test conducted at the Cotsen Institute of Archaeology at UCLA, Muros documented that Aquazol grade 200 begins to soften around 65% relative humidity in resin form, and around 70% in a film prepared at 40% in isopropanol and water. Arslanoglu had previously measured that at 75% or below, there is no significant loss of adhesion, and that above 84%, all grades gel.
This is not published by the manufacturer: it comes from conservation literature. And it doesn't make the material unsuitable: it means that in a space without climate control and with consistently high humidity, this is not the material. Preparing in isopropanol instead of water gives about five points of leeway.
The grade matters: 50 and 500 have different figures. The one described here is 200, and the difference between the three is explained in the Aquazol grades guide.
When NOT to use a consolidant
There are situations where the correct response is not to choose a better consolidant, but not to consolidate yet:
- When you don't know what caused the degradation. Consolidating over an active cause fixes the damage in place.
- When there are salts, rising damp, or movement of the support. The consolidant does not solve any of these three, and can worsen the first two by closing porosity.
- When testing in an inconspicuous area changes the appearance of the surface. A change in sheen or saturation in the test is a response, and the response is no.
- When the artwork has heritage value and you are not the one signing off on the intervention.
What not to do
Do not apply hot what dissolves cold. With cellulose ethers, heat works against solubility.
Do not extrapolate a concentration between brands or between grades. The valid figure is from the product data sheet you have. The same trade name can have grades with very different behaviors.
Do not work in an enclosed, unventilated space with solvent-based resins. The solvent doesn't disappear when the surface is no longer wet to the touch: Lascaux warns that complete evaporation can take days or weeks. In a chapel or an unventilated room, this is a safety condition, not a detail.
Do not consolidate for "insurance," just in case. This is the fastest way to an artwork saturated with material that nobody requested.
Frequently asked questions
What is the difference between consolidating and adhering?
Consolidating restores cohesion within a stratum that is pulverizing. Adhering reattaches a stratum to the one beneath it when it has lifted. These are distinct problems and require different materials, and confusing them leads to saturating a surface with product that only needed to be re-adhered.
Are consolidants reversible?
It depends on what is meant by reversible and when the question is asked. Cellulose ethers dissolve in cold water but become insoluble when hot, and Feller and Wilt documented for the Getty Conservation Institute that thermal aging can cause them to lose solubility. "Reversible" accurately describes the freshly applied film; it's not a thirty-year promise.
At what concentration should a consolidant be prepared?
The figure comes from the product data sheet you have, not from a general recipe: the same trade name can have grades with different behaviors. The common criterion is to start with the lowest concentration and repeat the application if necessary. Lascaux indicates this for Paraloid B-72, warning of the risk of saturation when over-concentrating.
Can I use Aquazol in a high humidity environment?
It depends on the grade and how much humidity. For Aquazol 200, Muros measured at the Cotsen Institute of Archaeology at UCLA that it begins to soften around 65% relative humidity in resin form, and at 70% when prepared in isopropanol and water. In a space without climate control and with consistently high humidity, this is not the material.
Why do some manufacturer datasheets not mention conservation?
Because what a manufacturer declares depends on who they manufacture for. A company that formulates for conservation writes it in its datasheet; a chemical company whose material reaches the sector repackaged documents its market, which is usually pharmacy, construction, or the chemical industry. That does not make a material suitable or unsuitable: it changes where the backing is, with the manufacturer or in Conservation-Restoration literature.
What you need to get started
The materials in this guide, in two blocks, because not all are available at once.
What arrives this week
It's in the warehouse, in short supply. If the order is for several jobs, please write to us beforehand and we'll reserve it.
- Klucel® G 500 g: cellulose ether for paper works and sensitive polychromy
- Aquazol® 200 1 kg: polyoxazoline soluble in water and alcohols
What is ordered from the supplier
These are supplied to order. Write to us and we'll confirm the lead time before you pay anything.
- JunFunori® Glas: for matte and powdery paint layers
- Tylose MH 300 P2: cellulose ether
Paraloid B-72, Lascaux Medium for Consolidation, sturgeon glue, rabbit skin glue, and wheat starch are ordered from their own product pages, linked above.
What this guide does not cover
- Relining and marouflage adhesives. Lascaux 498 HV, 303 HV, and 498 20-X are relining adhesives, not consolidants, and deserve their own article.
- Stone and stony material consolidants. This is another family and another problem.
- Polyamides and textile heat-seal adhesives. Outside the scope of this article.
- Diagnosis of specific artworks. None of the above replaces seeing the piece.
If you have a specific case
Tell us what the artwork is, what's happening to it, and its conditions. We'll tell you what to look at before buying anything.
Álvaro