Isolation Coats and Varnishing on Mixed Media Paintings

This blog post is primarily for students of the past Concept to Completion workshop, and for

those who recently attended the May 14th, OPUS Granville Island demonstration in Mixed Media on Panel and for all those past students of my Energizing and Experimental Abstract Painting Workshop with Acrylics and Mixed Media. And, lastly, for any artist who is interested in varnishing their paintings that contain mixed media.

To start, when I write here "mixed media" I am referring to a mix acrylics paints in all their forms (liquid, heavy body, ink and spray acrylics) as well as mediums that are polymer based including but not limited to molding pastes, absorbent ground, gesso, GAC products, polymer mediums, clear tar gels and so on. And also including but not limited to pencil crayons, inks, spray paint, pastels, water soluble pencils, and collage.

Lately I've been using quite a bit of chalk pastel to finish off my abstract paintings. In particular

I love the Senelier chalk pastels and after my demonstration at OPUS Granville Island last Saturday I purchased a whole bunch of Panpastel(TM) which I've never used before but am super excited to try on my on the dry textured areas of my mixed media paintings using my flat Robert Simmons 'Decorator' brushes. Whoohoo I'm excited!

This blog pertains to a question has come up in all these above mentioned products during demonstrations and workshops and that is, how do you final varnish a painting with a lot of mixed media, such as pastel, on it? The challenge is that usually you would lay down an *isolation coat (defined below) on top of your painting prior to putting a final coat of either polymer varnish or MSA (Mineral Spirit Acrylic) varnish. However, once you've added pastel if you like where it's located on your piece and you don't want it to smudge, you'd be leery to apply an isolation coat. So what do you do? I sent an Email to the technical team at GOLDEN paints and here's what they said.

Please note prior to reading this understand that trying the advice below which solves our/my

challenge of finishing off a mixed media painting was advice tailored to my needs and that each piece and each artist will present other needs and potential problems and for anyone interested in pursuing this approach should contact Golden Technical Support and always TEST before applying anything to a final, valuable piece as these steps are irreversible.

If you are first spray applying an Isolation Coat, of the GAC 500 and Transparent Airbrush Extender, then applying the Polymer Varnish should not be an issue since the dry media has been consolidated. The logic for this recommendation is in essence we are happy to offer Polymer varnish as a removable water-based varnish, however it is slightly more prone to color shift or slight ambering in time; so we are only comfortable recommending it for applications where full removal and re-application are a possibility.

For direct application to dry media such as pastel the MSA would a be a better option. Also, you are correct in the assumption that Polymer Varnish does not come in an aerosol can.

Isolation Coats are very useful for a standard acrylic painting as they allow greater options for future conservation. However once an art piece moves into mixed media or other unique process many considerations need to be weighed. These may include the look of a surface, or sensitivity of materials to various solvents.

Regarding the pieces you described water sensitivity and fragility of the media are the main concerns. Brush applying any coating over powder pastel, or charcoal has a risk of smearing or blurring the media. Thus, we typically suggest only spray applications directly to these surfaces. Take into consideration that applying any coating to a dry media will deepen and darken colors, a good analogy for this is how a river stone looks dark and glossy when we and grey and frosty when dry.

One option is to not apply an Isolation Coat and simply spray apply MSA Varnish (Gloss) in thin layers until the powdered media is fully sealed with an even gloss finish. Then the final sheen could be adjusted as needed with a reduced sheen varnish. This process would begin to mimic our recommendation for varnishing a watercolor which can be found here at

Another possibility is to use an Airbrush to spray apply GAC 500 mixed with Airbrush Transparent Extender at a ratio of 2:1. This mixture is our standard recommendation for a sprayable Isolation Coat, however since this is a water borne care must be taken in application to avoid runs and blurring the underlying media. Once the pastel is sealed then MSA or Polymer varnish could be applied as desired.

Finally there is an option of sealing the pastel with a few spray applications of MSA Varnish (Gloss,) allowing the piece to cure until the solvent odor had completely dissipated , then applying an Isolation Coat, and finally applying a final coating of MSA Varnish. The logic here is that having a full layer of an Isolation coat will hopefully protect the underlying media if a conservator ever needed to remove the top varnish. But it is a complex composite of coatings and you would want to leave documentation with the piece about the process you settled on.

As always please make some test panels before experimenting on a finished work. Once last point of information is that the processes mentioned above do no relate to the use of Oil Pastel which being a non curing media has its own set of concerns, and limitation for varnishing.

* isolation coat - An isolation coat is a clear, non-removable coating that serves to physically separate the paint surface from the removable varnish. The isolation coat serves two purposes: 1. To protect the painting if/or when the varnish is removed by separating the pigmented area of the painting from the solvents used in removal. 2. To seal any absorbent areas in order to create an even surface on which to apply the varnish.