A layer of varnish on a finished painting will protect it from dust, dirt, grease and UV rays. It will also even out any unevenness of sheen on a paint surface e.g. a gloss varnish will make the whole picture surface equally glossy. All solvent varnishes are made up of resin and solvent. The resin provides the stable, solid, fast drying and glossy component of the varnish, and the solvent the liquid vehicle, which evaporates in the air with time which allows the resin to solidify once more after the varnish application. There are 2 main types of solvent varnish - a final picture varnish, and retouching varnish. The difference between the two is that the picture varnish will have a greater resin to turpentine ratio than the retouching varnish. The reason why is that the picture varnish is designed to be more concentrated to form a more solid, continuous layer of resin over a finished work, the layer will be even in its appearance. Its strong, solid structure will not allow water or other liquids to permeate through it, and conversely will not allow any liquid still contained within any semi-dry oil colour beneath the layer of varnish to escape into the atmosphere. If a painting is not sufficiently dry when varnished with a final picture varnish blooming may appear, as well as more visible cracks in the varnish as the paint beneath shifts. This is why it is very important to not apply a final picture varnish until the painting is at least 6 months old. Picture varnishes should be removable so that they can be taken off and replaced with a new layer if the old layer gets damaged or dirty, and all good varnishes will state the best means of removing varnish (although it will be with the use of the solvent that is used in the varnish itself). Because retouching varnish has more solvent in it, when it dries liquids are able to permeate through the layer of varnish, which means that the painting does not need to be dry before its application. It is used as a temporary protection layer as well as a device to unify sheen during the painting process. Small quantities of varnish are also sometimes used in oil painting mediums to act as a siccative (to speed drying) as well as add a little more gloss to the finish. The resins used vary but typically it is damar resin if it is not a synthetic alternative, such as ketone. Damar resin is extracted from the Dipterocarpaceae family of trees in India and East Asia, and as well as in varnishes, can also be found in the binding of Schmincke Mussini oil colours. It is thought to increase the appearance of colour brilliance, and is a good ingredient in oil painting mediums as it has a good colour holding capacity. Generally speaking, damar is preferred to synthetic resin as it is thought to provide a deeper, more lustrous finish, as well as being less likely to yellow with time and having more stability. The solvents are either turpentine or white spirit, which dries slightly slower than turpentine. Winsor and Newton also offer a range of Artisan varnishes which are water-based and to be used to protect fully dried paintings created with the use of Artisan colours, and can only be removed with the special Artisan varnish remover.
All solvent varnishes can be applied with a spray or a thin flat varnish brush, and can be used on all dry oil, alkyd or acrylic works.
Good varnish vs bad varnish
Generally speaking, the logic behind considering what a good varnish is that it needs to be made of high quality ingredients that are compatible with the materials used in your work. The finer double rectified turpentines used in Michael Harding’s picture varnishes will have less impurities and therefore behave in a more stable way. Conversely, household varnishes will use less-refined white spirits which if used on paintings, would clearly deteriorate in appearance/yellow over time. Winsor and Newton use a higher quality grade of white spirit in their varnishes in order to produce affordable yet high quality varnishes. In Zest-It’s Dammar Retouching varnish Damar crystals have been diluted in the non toxic, environmentally friendly solvent. This means that the varnish is citrus smelling and has all the other qualities possessed by Zest It, including stability and resistance to yellowing (although there is a tint to the mixture in its fresh state). Shellac is a single component resin varnish which dries clear and is soluble in alcohol, and although it is a recognised varnish it is not commonly known to be used as a final picture varnish for oil paintings.
There is some debate about the synthetic ketone resin and its use in artist quality varnishes (that is may yellow over time and that it may be brittle when dry), but the general consensus by us at Jackson’s Art Supplies is that too many reputable manufacturers, such as Winsor and Newton, C. Roberson and Co and Royal Talens, are using it for question marks over its suitability as a long term varnish to be taken too seriously. Ketone dries glossy and solidly and does not absorb water. Jackson’s Art Supplies realise the importance of using a high quality varnish to serious artists, and this is why we only offer the best varnishes available on the market today.
Matt varnishes can be made 2 ways – either with the use of a wax that is matt anyway when dry, or by adding a matting agent to a varnish that would otherwise dry gloss. Michael Harding’s matt varnish is made with beeswax and double rectified turpentine, and C. Roberson & Co also produce a similar beeswax picture varnish. C. Roberson and Co’s ‘Matt Varnish’ contains a petroleum based microcrystalline wax, which is elastic and adhesive in its nature, as well as matt in appearance. Matt varnishes by Royal Talens and Jackson’s Art Supplies contain a matting agent (in the case of Royal Talens they use silica), which serves its purpose but the only snag is that the matting agent tends to be marginally denser than the other ingredients in the varnish and will sink to the bottom of the bottle over time. This may lead to an uneven sheen, so it is absolutely vital to give your bottle of matt varnish a thorough stir or shake prior to use.
Winsor and Newton state the following advice on how to apply varnish.
With a brush
1) Use a 1”- 4” flat wide, soft, tightly packed, varnishing brush (such as the Winsor & Newton Monarch glazing/varnishing brush). Keep it clean and use it only for varnishing.
2) Place the work to be varnished flat on a table - do not varnish vertically.
3) Apply the varnish in 1-3 thin coats, rather than 1 thick coat. A thick coat will take longer to dry, may dry cloudy, drip or sag during application and has a greater chance of showing brush strokes when dry.
4) Thinned varnish is more susceptible to producing bubbles. Do not be vigorous in your application.
5) Apply in long even strokes to cover the surface top to bottom while moving from one side to the other. While working, inspect the varnish layer at all angles for bubbles. Even them out immediately.
6) Once you leave an area, do not go back over areas that you have done. If you do, you risk dragging partially dry resin into wet, which will dry cloudy over dark colours. If any areas were missed, allow to dry completely and re-varnish.
7) After varnishing, it is recommended that the surface should be shielded from dust with a protective plastic film “tent”.
Applying Varnish using a spray can
1. Try not to store aerosols below 15'C (59'F) - if they have been stored around this temperature - do not use them until they come up to ambient again - all aerosols contain a mix of product and propellant - at lower temperatures the products wants to "drop out of solution" and so could either block the nozzle, or worse, come out of the nozzle as "blobs of product" which then fall on the work itself.
2. Always shake the container vigorously before use to ensure the contents are homogenous.
3. Always hold the container upside and spray for a couple of seconds - this will send a spray of propellant only out of the nozzle and clear it
4. Always do this at the end of use as well to clear the nozzle of material build up.
5. Be careful if using the container extensively over a short period of time as the contents temperature will drop with a potential for the product to "drop out of solution" - this applies to all aerosols but is only likely to be noticed during extensive use.
6. Always spray with the can almost vertical and allow the contents to "cascade onto the work".
7. When spraying the can is to be held at least 25-30cm (10-12 inches) away from the work.
8. Mount the work onto "waste material" and spray side to side beyond the extremities of the work to ensure full coverage.
9. For porous, unprimed surfaces such as card, canvas, hardboard, plaster etc. apply a thin layer of gloss varnish before applying any matt or satin varnish.
Making your own Damar Varnish
It is both cheap and easy to make dammar varnish, to use either as a retouching varnish or a final picture varnish. It is a case of diluting one part dammar crystals to one part turpentine. Wrap your crystals in a piece of cheesecloth or muslin and tie at one end, and suspend in a jar of your solvent. As I said earlier, the more refined the solvent the easier to use the varnish, so try and use something that has been rectified or distilled of its impurities. You will need to gently stir every now and then for the following 2-3 days, as the crystals break down. After about 3 days all the crystals should have dissolved and you then have your damar concentrate. With this you can either a) make picture varnish, by mixing
1 part damar concentrate to one part solvent, or b) make retouching varnish by mixing one part damar concentrate to 3 parts turpentine.
You may also make a matt varnish by also diluting a quantity of beeswax in the same jar of damar concentrate.