Here’s some info about my experience with stacking varnishes to share with the group:
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I’ve changed my varnishing method recently and wanted to share what I’ve learned. Please know I’m not claiming to be a varnish pro or have any special knowledge about varnishes- this is just my experience. Varnish will behave differently according to many variables such as substrate, temperature, application, paint film and drying times — your results may vary.
I have used Conservator’s Products Varnish for years- it comes in gloss and matte, and you can mix between the two to create your own finish. I prefer an almost matte finish in a ratio of 4:1, matte to gloss. It’s easy to remove in the worst case scenario, and not too smelly. But, I was never entirely happy with the uniformity of the finish, especially in raking light.
I listened to a varnishing webinar with George O’Hanlon where isolating varnish was discussed, and it seemed like the answer to my problem. Using a two layered process of varnishing is called ‘stacking’- it works because each varnish is made up of different resins, and they can be applied on top of each other without activating the layer below. Natural Pigments Conservar Isolating Varnish is a synthetic resin made from laropal, and Conservator’s Products varnish is made from regalrez. Using the isolating varnish first gives a much more uniform finish to the final varnish.
It seems counterintuitive, but you can and should (according to Mr. O’Hanlon) put a matte varnish over the isolating varnish layer. Normally I would worry about this- the isolating varnish is a bit shiny, and the matte is, well, matte- and one would worry about adhesion in that scenario. They suggested matte varnish over the isolating in the webinar, and I contacted Natural Pigments to make absolutely sure this was sound practice.
Stacking Varnishing Tips:
I like to have a dedicated brush for each varnish. The laropal makes the brush very stiff after cleaning, unlike the regalrez. Some painters do not wash out their varnish brush, preferring to reactivate it in varnish, but I haven’t tried this yet. Isolating varnish is also VERY smelly— I don’t use it in my studio. Plan accordingly.
Isolating varnish should be applied to a dry painting, and you should wait a minimum of three days before adding a final varnish. Be careful with application: I had a scary thing happen (see photos) where I accidentally flooded the surface with a heavy brush load and the isolating varnish dried blotchy; it looked almost like a bloom. Luckily, the final varnish smoothed it out and it looks good now, but something to be aware of.
If you choose Conservator’s Products as a final varnish, buy the gloss and matte and make a scale. I keep dedicated measuring cups so I can mix the same ratio consistently. This varnish should be mixed as you need it- not made ahead in a batch, so you’ll need to measure and mix every time.