A conservation varnish is not just any varnish. Unlike decorative or industrial finish varnishes, those used in conservation and restoration must meet strict technical requirements: reversibility, long-term chemical stability, and compatibility with the original materials of the artwork.
The use of an inappropriate varnish can cause irreversible damage: premature yellowing, loss of chromatic saturation, difficulties in future interventions, or, in the worst cases, direct damage to the paint layer. For this reason, choosing correctly is not a minor detail.
Retouching varnish and protective varnish: an essential distinction
Before delving into types of varnishes, it is essential to differentiate between two concepts that are often confused:
Retouching varnish: applied to specific areas during the chromatic reintegration process to unify the surface's absorption and facilitate color perception. It is applied very diluted, in thin layers, and is not intended as a final protective layer.
Protective varnish (or final varnish): applied as a finishing layer over the consolidated and reintegrated artwork. Its function is to protect the surface from oxidation, dirt, and light, and to unify the visual finish. It must be reversible, stable, and compatible with future interventions.
Using a retouching varnish as if it were a protective varnish—or vice versa—is a common mistake that compromises both the visual result and the integrity of the artwork.
Types of conservation varnish by composition
Ketone resins: Laropal A81
Laropal A81 (BASF) is the current benchmark in the restoration of paintings on canvas and panel. It is a low molecular weight ketone resin with exceptional characteristics:
- High reversibility: soluble in low-polarity solvents (Shellsol A100, refined white spirit)
- Excellent stability: minimal yellowing, proven performance in leading museum collections
- Finish: can be formulated in different degrees of gloss depending on dilution and application method
It is the recommended varnish for interventions on paintings on canvas and panel when the maximum guarantee of reversibility and durability is required.
Hydrocarbon resins: Regalrez 1094
Regalrez 1094 is an aliphatic hydrocarbon resin with properties very similar to Laropal A81 in terms of stability and reversibility:
- High reversibility: soluble in Shellsol and low-polarity solvents
- Excellent stability: very good aging performance, without significant yellowing
- Finish: glossy — this is a point to consider, as it does not easily allow for a matte or satin finish without specific additives
A solid alternative to Laropal A81 when a glossy finish is desired without compromising reversibility.
Natural resins: dammar and mastic
Natural resins have been the standard varnish for centuries, but they have limitations that make them problematic for contemporary restoration:
Dammar: soluble in aromatic solvents, it provides a glossy finish with rich chromatic saturation. However, it yellows over time and can become difficult to remove without risk to the paint layer in future interventions.
Mastic: a Mediterranean resin with characteristics similar to dammar. Same aesthetic advantages, same stability limitations.
Both are still used in restoration—especially in varnish retouching and as components of traditional mixtures—but they are not the first choice for permanent protective layers on heritage artworks.
Acrylic varnishes with UV protection
There are varnishes based on acrylic dispersions that incorporate UV filters, designed to protect the artwork from ultraviolet radiation. Their use may be justified in specific contexts (works on paper, photosensitive pigments), but it should be noted that their reversibility with mild solvents is limited compared to ketone or hydrocarbon resins, which can complicate future interventions.
Key criteria for choosing the correct varnish
| Criterion | What to evaluate |
|---|---|
| Reversibility | With what solvent is it removed? At what concentration? With what risk to the original? |
| Stability | Does it yellow? Does it lose reversibility over time? Is its aging documented? |
| Finish | Matte, satin, or glossy? Is the finish adjustable or fixed? |
| Compatibility | Compatible with the painting technique and retouching materials used? |
| Application | By brush, bristle brush, or spray? Does it require prior dilution? |
Comparative table of conservation varnishes
| Varnish | Base | Reversibility | Finish | Stability |
|---|---|---|---|---|
| Laropal A81 | Ketone resin | High | Satin / glossy (adjustable) | Excellent |
| Regalrez 1094 | Hydrocarbon resin | High | Glossy | Excellent |
| Dammar | Natural resin | Medium | Glossy | Medium (yellows) |
| Mastic | Natural resin | Medium | Glossy | Medium (yellows) |
| UV Varnish (acrylic) | Acrylic dispersion | Medium-low | Variable | Good (UV filter) |
Note: Paraloid B-72, though widely used in conservation, is a consolidant and adhesive, not a protective varnish. It should not be used as a finishing layer in easel painting except in specific and documented applications.
Varnishes available at Innovart
At Innovart, we offer a selection of varnishes and base materials for the usual needs of a conservation workshop:
MIR Line:
- MIR Retouching varnish — for unifying absorption during the chromatic reintegration process
- MIR Glossy varnish — a common finishing varnish used in fine arts and restoration
- MIR Venetian turpentine — solvent and traditional component for custom formulations
Resins and base materials for custom formulation:
- Paraloid B-72 — an internationally recognized acrylic consolidant. Soluble in acetone and ethanol. Use: fixing paint layers, not as a finishing varnish.
- Paraloid B-44 — a more rigid variant, for consolidating hard surfaces
- Dammar granules — natural resin for custom formulation of traditional varnishes
- Mastic — Mediterranean resin for traditional-based mixtures and retouching varnishes
- UV Varnish — for additional protection against ultraviolet radiation in specific cases
How to apply a conservation varnish
Some basic application recommendations:
- Environmental conditions: relative humidity between 40-60% and temperature between 18-22 °C. Avoid drafts during drying.
- Clean and dry surface: varnishing is always performed on a clean, stable, and completely dry surface.
- Dilution: resin varnishes are generally applied diluted. The usual concentration for a protective layer is between 10 and 25% by weight, depending on the resin and desired finish.
- Application method: soft brush (sable hair or similar) or spray gun. Spraying reduces the risk of disturbing underlying retouching.
- Thin layers: two thin layers are better than one thick one. Respect the drying time between layers.
Frequently asked questions about conservation varnishes
Can I use any artistic varnish to restore an artwork?
No. Conventional fine art varnishes are not formulated with the reversibility and stability criteria required in conservation. For heritage artworks, always use specific and documented varnishes.
How often should a restored artwork be varnished?
It depends on the exhibition environment and the varnish used. Modern ketone or hydrocarbon resin varnishes perform stably for decades under suitable conditions.
How do I remove an oxidized varnish?
Using solvents of appropriate polarity, always with preliminary tests in an inconspicuous area and with the corresponding PPE. If in doubt, consult us before intervening.
Do you have a specific case and don't know which varnish to choose? Contact us — we will advise you without obligation.