Choosing the right putty to fill a loss is one of the most frequent decisions in restoration. A mistake here can compromise the mechanical stability of the treatment, alter the visual reading of the artwork, or, in the worst case, damage the original layers. In this guide, we review the most commonly used putty types in conservation-restoration, their properties, and when each one is appropriate.
What is restoration putty and what is it used for
Putty is the filling material used to volumetrically reconstruct lacunae, losses, or missing parts in pictorial layers, supports, or polychromy. Its function is twofold: to mechanically stabilize the affected area and to create a base surface on which to apply chromatic reintegration.
A good restoration putty must meet the following criteria:
- Mechanical compatibility with the original support
- Reversibility: capable of being removed without damaging the original
- Long-term chemical stability (no volume changes, no acidity)
- Suitable surface for receiving retouching color
Most commonly used putty types
Traditional protein putties
The classic formula of animal glue (rabbit skin glue or hide glue) with mineral filler (calcium sulfate, calcium carbonate, or whiting) remains the benchmark for old works on panel or canvas with traditional preparation. They are compatible with original materials, respond well to humidity changes, and allow for work in several layers.
When to use them: works from the 13th to 19th centuries with gypsum or carbonate preparation. Ideal when maximum historical compatibility is sought.
Limitation: they are hygroscopic. Not recommended in environments without climate control.
Modostuc
Commercial putty based on calcium carbonate and polyvinyl acetate (PVA). Widely used for its ease of application and good surface finish after sanding.
When to use it: small to medium losses in works on canvas or panel where maximum reversibility is not required.
Limitation: PVA ages and becomes less soluble. Avoid for works of high heritage value.
Polyfilla Conservation Grade
Fine-grained acrylic plaster-based putty. Good dimensional stability, low shrinkage upon drying. Can be applied in thin layers and sanded to achieve very controlled textures.
When to use it: flat losses in contemporary painting or where a very precise finish is needed. A good general option for C&R.
Lascaux Gesso and Acrylic Ground
High-quality acrylic preparations formulated for conservation. Demonstrated stability, good adhesion, optimal surface for acrylic or aqueous retouching.
When to use them: contemporary works, new preparations, or when high technical demands are required.
Quick comparison
| Putty | Base | Reversibility | Ideal for |
|---|---|---|---|
| Animal glue + filler | Protein | High (hot water) | Old works, panel, historical canvas |
| Modostuc | PVA + carbonate | Partial | General use, small losses |
| Polyfilla CG | Acrylic plaster | Good | Flat losses, fine finish |
| Lascaux Gesso | Acrylic | Limited | High technical demand, acrylic works |
Application tips
- Substrate moisture: slightly moisten the loss before applying protein putties to prevent them from absorbing too quickly and shrinking.
- Thin layers: several thin layers are better than one thick layer. This reduces shrinkage and gives greater control over the final level.
- Finish level: the putty should be slightly below the original level so that the retouching does not sit on top of the paint.
- Isolate before retouching: a layer of varnish or consolidant between the putty and the retouching prevents color migration and facilitates future removal.
In summary
There is no universal putty. The choice depends on the support, the age of the artwork, the conservation environment, and the type of retouching to be applied. The key questions are always: what level of reversibility do I need, and what original materials am I working with?
At Innovart, you will find the main filling materials used in professional conservation-restoration. If you have any questions, write to us at info@innovart.art — we respond with technical expertise within 24 hours.