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Technical Notes on Fine Art Painting

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Reasons for an

Isolation Coat

My paint washes were inadequately bonded with the canvas.  This would not  not allow a direct application of a final varnish.  If this is an archival varnish it would someday require removal or replacement with special chemicals that would likely act on the paint. To prevent this and to protect the painted surface, coats that fix the paint and seal the surface must first be applied.  The sealing also ensures that subsequent coats of medium or varnish produce an even surface.


The first thing to do is affix the paint to the canvas, then ensure that it is sealed so that the entire surface has an even gloss (evenly absorbant) and in the process, create a layer between the painting and the final varnish.  This inbetween layer forms the isolation coat. Isolation coats must be gloss in order to remain clear.  The final (archival) varnish, consisting of one or more coats, may be gloss or satin or matte but one layer in itself can determine the level of surface reflection.

Condition of the Painting

The varnishing of each painting should be considered on its own merits. The particular choice of isolation coat should address the characteristics of each work.  My particular example follows:  

I have an acrylic painting which contained painted areas that were slightly glossy while the rest (mostly background) are washes on an underprimed cotton canvas.  The use of washes is not only the intended effect but part of the process of this painting’s development.  The blurred, sunny effect of a high minor tonal key would be compromised by thickly painting the flat larger areas that exist on the subject and ground. I was aware that the washes may not have been sufficiently bonded with the canvas even though during application they had soaked into the canvas fabric.

In good light the surface was inconsistent and I wanted to alleviate the contrast between the glossy paint with the dry, matte areas.  In any event, the end result should not be glossy enough to produce a glare.   At  the start, I was unsure of how much matte or satin, the final varnish would require.

I hope you will understand my material choices in light of the intermittent goals set for each stage.  Isolation coats on most paintings shoul;d be easier than this.


Do not use a dust encrusted vacuum nozzle if your canvas has any texture whatsoever.  You will add dust and hair to your painting.  Better to use the cold plastic edge of a shop vac.  Sometimes wiping with a micro fibre cloth does some good even while applying the gel.  While still dry, a lint roller will do wonders. A needle imbedded in a wood handle or a cutting blade can come in handy.  As well, a water spray bottle if you have to wipe it off before reapplying one of the coats.  If your painting and canvas are constructed really well, you could just shower the surface in the bath tub, but yours is probably not so well constructed and advise you not to.

FIRST COAT used by me consisted of Grumbacher Permanent Gloss Varnish thinned by one third distilled water and applied with a sponge brush with the canvas layed in a horizontal position. Ensure no foam or bubbles.  Inspect for complete coverage and then air dry.  This coat serves to fix the paint washes to the canvas and stiffen the canvas weave with much the same effect as a priming coat has on a raw canvas.


Sponge-backed sandpaper (3M Super Fine - made in England) was used to lightly sand the rough surface before applying the next coat. This is so your sponge brush will not be shredded in later applications.  I applied the second coat of the same permanent varnish to the dry-looking background areas only.  These areas need more varnish because they are more absorbant.
Together the first two coats prevent subsequent coats of gel from soaking in. In the case of a coat containing a matte additive,  uneven distribution of the matte additive collecting on the surface will be avoided.

THIRD COAT is a foam brush application containing about 2/3 Golden Self Levelling Gloss Gel and one third thinned varnish mixture from above.  Golden Soft Gel has been recommended elsewhere and could be used in place of the levelling gel that I have used.

FOURTH COAT consists of the same gel mix but was applied with a wide #50 Simply Simmons synthetic brush to make the coat thicker. The purpose of both coats of acrylic gel is to:


Bathed in Sunlight 24X36"

Acrylic Painting (cropped)

1. Form the isolation layer separating the removable varnish from the painting surface.  

2. The objective is to even out the glossiness of the canvas surface before applying the final varnish.  I highly recommend using a thinned gloss gel because it is clear and the evenness of a gloss surface will ensure that any non-gloss varnish applied later will also be absolutely even.


This is the removable or archival varnish.  Golden Polymer Varnish with UVLS (Satin). It may be slightly thinned with distilled water but I found it unnecessary.  I shook it to disperse the matte additive and banged it down on a hard surface a few times to get rid of the bubbles.  My foam brush applied it so effectively that only one coat was needed. The reduction of glossiness provided by one coat was sufficient.  The intent of the method used here is to keep the effect of the overall coatings relatively clear by using only a single satin application as the final layer to reduce the glare on the surface coat. The purpose of the final varnish:

 1. To apply the same level of satin sheen evenly throughout the entire painting surface. A patina will result.

 2. With satin or matte varnish, diminish the glossy reflection and glare created by the underlying isolation coat(s).

 3. Provide a removable/replaceable varnish which is less tacky and attracts dust much less than the acrylic gel.  

 4. Protect with a UV filter and provide a barrier against reactants in the atmosphere.

Tasks or Goals