Varnishing
Ask any painter, and the one thing we all fear, dread and send up that big old river of denial is varnishing. It is the one sure fire way to completely ruin a painting and I can’t think of another aspect of fine art that provokes more stress and intimidation. The fact is that all paintings, whether oil or acrylic should be varnished. Many people think that acrylic doesn’t need a varnish, but the large polymer chains that make up an acrylic emulsion actually have an open, lacy structure that can easily trap dirt. In addition the softness of the acrylic resin is easily scratched, so it is important to protect the surface of the actual paint with a barrier layer that a conservator could remove and replace at some point in the future. Oil paintings need a protective coating for the same reason, but offer a greater challenge as oil paints can take months to technically “dry”.
Oil paints dry by oxidation, a chemical process in which the paint absorbs oxygen from the atmosphere, then goes through a chemical change, which releases the oxygen leaving behind the tough, elastic material linoxin. This “exhalation” of oxygen can take several months if the paint is applied thickly, and when a varnish is applied while the painting is still drying the oxygen can become trapped underneath the varnish coating. This can result in “bloom”, where flowery occlusions will develop, or as I found out personally, in a section of the paint which becomes sticky and never actually dries - which always makes me think of the David Bowie song on “Hunky Dory” where he sings about “a funny old crib on which the paint won’t dry”. Choices for varnishes further complicate matters. Basically, there are waxes or resins as options, but the types and variations can seem limitless, and we frequently find artists gazing perplexedly in our varnish section. Then there is the additional question - to brush or to spray? Spray varnishes offer a convenience and often make it easier to apply very thin coats that leave brushstrokes and textures looking as they were when the work was completed. Aerosol cans present health hazards, and one should always use a respirator when spraying, and make sure there is good ventilation. Temperature is also important when varnishing, and one should avoid applying a varnish on cold, damp days.
As to material choices, technically a varnish is a final coat which is designed to even out gloss, and allow colors to “bear out”. It should also be removable, so an application of an alkyd resin, such as Gamblin’s Galkyd is not suitable as a varnish. Acrylic resins come in several forms - water soluble, l based and low molecular weight acrylic. This last type results in a thinner coating, appearing less like a heavy, plasticized coating. I have experienced the most problems with water based acrylic varnishes, and one should be sure to use distilled water when thinning these coatings, as the metals and chlorine in tap water can cause the varnish to appear cloudy. Thinning acrylic varnishes can create many small bubbles which can show up on your painting so it is advisable to let your varnish settle for an hour after thinning.
My preferred final varnish is wax. It is the easiest coating to remove, as it can simply be wiped off with a clean, lint free rag with solvent, and it results in a satin finish that leaves a painting looking very natural, as if it had no coating at all. Most resin varnishes tend to have a slight electrostatic charge to them and so they attract dust - a characteristic which wax does not have. Wax can be prone to glossing up if it is frequently dusted with a rag, and it can soften on hot days, to the point of leaving fingerprints if touched - but then, you shouldn’t be touching paintings anyway! Final thoughts - always keep a pair of tweezers handy when varnishing to easily remove dust or stray hairs that might fall into your surface; make sure you have a very good, adjustable light source so you can use the glare to check the evenness of your coating; arrange to have a clean, dust free area set aside in advance for your painting to dry; have plenty of clean, lint free cloths, solvent, and a soft, fine bristled varnish brush handy; and make sure the surface of the painting to be varnished is clean and free of dust and dirt. Good luck! And if you have any problems, then get into a Utrecht Art Supply store and we’ll help you solve the problem.
June 10th, 2008 at 1:12 pm
Hi,
I was wondering if you know what product to use to apply over acrylic or oil paintngs to get a high gloss finish? I have seen some artist’s work and it says it has a “resin finish.”
I would be painting on a hardboard frame as opposed to a canvas.
Thanks,
Catherine
June 11th, 2008 at 11:26 am
All paintings, whether acrylic or oil should be varnished to protect the surface of the painting and facilitate cleaning. There are a multitude of coatings which can be applied to either oil or acrylic works, and it is up to the artist to decide which is best for the final appearance they want. There is a popular trend to pour thick, high gloss resin over artwork to create a heavy coating, but this should not be thought of as a varnish, as it would not be easily removed. We sell a product called Envirotex, which is a two part epoxy resin, and it creates a thick, glossy surface. Unfortunately these types of resins will often yellow over time, so they should not be thought of as archival finishes for fine art.
For archival, fine art applications, one can apply acrylic or natural dammar resins to obtain a high gloss finish. Dammar is a tropical tree resin which is disolved in turpentine and is easily removed by conservators. It can be applied in multiple coats to create a high gloss finish. Acrylic resins are not as easily removed as dammar, and can be more prone to scratching. They are available in both water soluable or solvent based formulas, and in my experience, the solvent based varnishes tend to perform better. I recommend using distilled water if you are using the water soluable variety, as the chlorine, metals and minerals in tap water can cause acrylic varnishes to turn cloudy. We always tell artists that varnishing is a challenging, difficult task and recommend you experiement before attempting a final varnish on a prized work.