Why varnish a painting?
The answer may seem obvious: to achieve a glossy, matt or other effect finish, but that is not its main function.
Varnishing is essential to preserve and extend the longevity of your artwork.
Traditionally, it has been used to protect surfaces from dust, light, humidity and other corrosive and environmental agents that can deteriorate them, but nowadays its boundaries go far beyond that.
In addition to conservation, artists use varnishes to add depth, to saturate and unify colours, to create gloss or, conversely, to remove it.
There are an infinite number of varnishes to use depending on the material we are using, and this is the first thing to bear in mind when buying.
Which varnish should I choose?
First of all, we can classify them by the type of final gloss they provide:
- Gloss or shiny: provides high shine.
- Satin: intermediate shine, very subtle.
- Matte: completely eliminates shine, creating a slightly more opaque finish.
Secondly, just as important as the previous point, we will choose a varnish that is suitable for the material we are working on:
- Oil: almost essential for conservation. Oil-based paints tend to oxidise when they come into contact with oxygen and turn yellow over time, as well as cracking. A sufficiently resistant varnish can preserve the work for centuries.
In the case of oil pastels, since they never dry completely, it is very important to protect them with a specific varnish. - Acrylic: as a relatively new pictorial medium, its behaviour over a long period of time is unknown. The oldest acrylic works are now beginning to reach 70 years of age.
Even so, it will undoubtedly provide the same beneficial characteristics in most cases. It protects, evens out colour and reduces tackiness. - Watercolour and gouache: as they are made on paper, they are very likely to get stained or wrinkled, as well as being impossible to clean. That is why they are usually framed with glass, but nowadays it is increasingly common to add a layer of varnish for the same reasons.
- Dry techniques: usually in spray format as they could be damaged by spraying liquid directly on them. They can be used to give a creative touch to your artwork, but mainly for preservation and to prevent pigment dusting and staining.
- Natural and untreated surfaces: such as wood, cardboard and other porous materials. Depending on whether they are outdoors or indoors, it is always advisable to protect them and they are suitable for almost all varnishes.
- Non-porous materials: plastics or substitutes, glass and others. They need specific varnishes or resins, which have that power of adhesion to be able to protect, especially from scratches, without peeling off.
Varnishes according to their composition
We can also differentiate them by their components. In these times when ecology and the environment are so important, less aggressive but equally resistant alternatives are being created, as well as being more affordable:
1.Oil-based varnish: composed of natural oils, resins and solvents. It is very durable and elastic, water-resistant. Used in oil painting. Its main disadvantage is its toxicity and difficulty in cleaning.
- Universal final varnish: protects and revives colours.
- Dutch Varnish: for final and intermediate use. It gives a glossy, powerful finish, enhances the colour and is harder and more flexible than others.
- Dammar: not very recommendable as a final coat due to its tendency to yellow, but excellent for intercoatings.
- Touch-up: to continue working on works that are already dry. It evens out the gloss and can be overpainted.
2. Water-based varnish: made of acrylic polymers and water. Very resistant and elastic, and less, if at all, toxic. It also has good elasticity and is ideal for interiors. It is used in water-based paints and dry techniques.
- Acrylic varnish: tends to be more innocuous on all types of paints and surfaces. Transparent, it is not noticeable when applied on white surfaces. With a high gloss finish and superior elasticity.
- Polyurethane varnish: made from synthetic resins. Extremely durable, with excellent water resistance and UV protection.
- Alkyd varnish: uses alkyd resins as a base. Good adhesion and ability to provide a smooth, glossy finish.
3. Solvent-based varnish: Resistant and high gloss finish, but emits toxic fumes and requires longer drying time. Suitable for oil-based media.
4. Resins: very resistant but toxic. Completely transparent and glossy finishes. Suitable for all types of media
- Shellac: composed of natural resins and solvents. It is very water resistant, but scratches easily.
- Lacquer: made from a mixture of synthetic resins and solvents. It has good durability, UV protection and water resistance, making it ideal for both interiors and exteriors.
- 2-component varnishes: the most resistant. Once dry, it encapsulates the work, protecting it from any external agent. It does not spoil easily. Suitable even for prolonged outdoor use. This option should be chosen when we are particularly demanding in terms of protection or when resistance to solvent products is required. Its main disadvantage, apart from its toxicity, is its high cost and difficulty to mix it successfully. Also, the waste of product, because once mixed, what is not used will be unusable.
Finally, depending on the comfort you are looking for and the specific final finish, you can choose your varnish in different formats:
- Liquids: to apply directly or with a brush. Some marks may remain after applying several coats.
- Gel: similar to the liquid varnish, it allows you to go deeper into the pores of the canvas in a more effective way.
- Spray: clean and easy application. It does not leave marks and allows several coats to be applied.
We hope that this brief summary of the options and characteristics to consider when varnishing has helped you to clarify your ideas.
Of course, everything is relative and all processes depend on multiple factors. It's just a matter of trying.
If you want to know more about varnishing, check out our other posts!
