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MITRA Forum Question Details

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  • longevity of oil mediums over acrylicApproveRejectUn-ApproveSubscribeUn-Unsubscribe
    Question asked 2018-01-10 18:07:22 ... Most recent comment 2018-01-11 15:57:50
    Varnishes Art Conservation Topics

    ​I would like to know if I need to prepare an acrylic painted surface for oil crayons to make it stable over time, and the best medium to seal the final surface.

      Also, is clear gesso the best medium to use over acrylic to prepare the surface for cold wax, what do I need to add to a low ratio of paint to wax? Do I understand correctly that using less than 2/3 paint to 1/3 wax is inadvisable without adding other mediums? I have found recipes online but no consensus.

    Thank you

Answers and Comments

  • EditDeleteModerator Answer

    There are a lot of variables in this proposed application. By "oil crayons" do you mean oil paint sticks, or oil pastels? This is important, because oil paint sticks dry like tube paints, but oil pastels are made using a non-drying vehicle and will stay soft indefinitely.

    Most of the time, it's possible to apply oil paint directly over acrylics, which generally offer enough absorbency and texture to support adhesion. A layer of clear "gesso" might unify absorbency and tooth across the entire surface, so that could be a good strategy if there are thinly painted or very slick passages in the underpainting.

    1/3 wax by volume sounds like a lot. Personally, I wouldn't apply a solvent-borne varnish over paint with that formula due to concern that it may be too soluble even when dry.

    Matthew Kinsey, Utrecht Art Supplies
    2018-01-10 20:34:48
  • EditDeleteModerator Answer

    Matthew, you beat me to this. I agree with you on this and the need to understad what is meant by oil crayons.

     Paint that contains as much as 1/3 wax should probably not be considered traditional oil paint. It would be better to avoid varnishing such works as the solvents required to remove that varnish in the future would very likely bit into and remove some of the original paint.

    If you decide to varnish, make sure that it is a varnish that is known to yellow the least and make sure that you record your paint media and varnish on the reverse of the painting (on the stretcher bars, etc) to make sure that future conservators understand what is in your painting and avoid testing the varnish with solvents likely to harm your paint.

    Oil paint with more than 1/3 wax should probably be considered an oily encaustic medium rather than the other way around.

    Brian Baade
    2018-01-10 21:36:33
  • ApproveRejectUn-ApproveUser Comment

    I was curious about both, but didn't know how they differed. I work in acrylics and have recently introduced applying different media on top of it​.  I always worry about whether oily media will adhere to the acrylic over time, and if I can do something to encourage that to happen. It's good to hear oil will adhere to the acrylic. I didn't think that was the case.

    My question about the cold wax was not clear, apologies. I am looking at it as an encaustic medium, to be applied over acrylic paint. This is where I would apply the clear gesso, between the acrylic painted surface and the wax medium.  The ideal would be traditional encaustic, but I work and live in a small space.  My confusion comes with so many conflicting views on how to use cold wax. My impulse would be to use layers of mostly wax and very little pigment, but some sources make it sound like you need to add Galkyd and/or various other gels to that mixture in order to make it stand up to time. 

    I just hate finding out too late that a piece I love will not stand up to time. I come from a background of using many non traditional materials, and am pretty familiar to mistaken assumptions about what is compatable over time. Thank you for your response.

    2018-01-10 22:57:27
  • ApproveRejectUn-ApproveUser Comment

    Interjecting a question here about the use of Clear I understanding right that using a layer of Clear Gesso between an acrylic underpainting and further oil paint layers is a good practice to insure long-term adhesion? Thanks so much for the clarification!

    2018-01-11 11:31:05
  • EditDeleteModerator Answer

    First, I need to be honest; I have no experience with clear gesso. I am immediately annoyed by the use of the term “gesso” for such a material but I understand that I am never going to win that battle.

    It is my understanding that clear gesso is intended to allow for a sizing/ground that allows the artist to exploit the color of the substrate and not obscure it with a more traditional colored ground.

    I am confused as to how this would promote better adhesion between acrylics and oils. Is the thought that the clear gesso adds some texture/mechanical tooth for the oil layers to adhere to? It seems to me that to remain clear, the amount of bulking filler and texturizers would have to be very low and unlikely to offset the diminishment of surface texture caused by the addition of the clear gesso layer.  Generally, the more layers, the more likely there can be adhesion problems.

    Others more familiar with the material may be able to comment with more authority.

    Brian Baade
    2018-01-11 12:01:07
  • EditDeleteModerator Answer

    ​A lot of moving parts to this discussion but let me jump in and provide some additional thoughts.

    As simply a separate question, divorced from the use of wax and speaking in general, we feel that oils will adhere to acrylics and all our testing has supported this. However let me throw in a few caveats. One, we know oil paints containing zinc have been linked to cases of delamination, including from acrylic grounds, and would recommend not using any oils that contain zinc - especially in an underlying layer. Two, while we believe and have tests showing that oils adhere to even glossy acrylic films (for example, oil grounds adhere well to our GAC 100 used as a size) we also know that in ANY system, including oils to oils and acrylics to acrylics, matte and toothy surfaces provide maximum adhesion. That is simply a function of increased surface areas and opportunities for mechanical adhesion through a 'lock and key' mechanism. Because of that, we tend to err on the side of caution and are one of those companies that often do suggest using a layer of acrylic matte medium as a form of translucent ground. We do not use the term 'clear gesso' but are aware that other companies do - but keep in mind those are not really clear but are essentially variations of a matte medium or a slightly more translucent version of molding paste. In any case, the role this is playing is mostly to make sure you have a uniform surface to work on top of, avoiding the inevitable issue of having an underpainting that is more absorbent in one place than another, or - which is often related - has a range of different sheens. Plus we never know which paints one might be using, so having this translucent ground layer helps assure that the paints are anchoring to one companies' product, making it easier to troubleshoot. For more information about our thoughts on oils adhesion to acrylics, please see the following article:

    Using Oils with Acrylics

    Moving on to the question about the use of cold wax techniques on top of acrylics, we would approach that with a lot of caution and would need to be comfortable both doing some testing as well as simply taking on a host of unknowns as this is simply not an area that has been looked into, as far as i know. What I can share is that we know encaustics do not adhere well to acrylics, except with highly textured grounds, or onto special very absorbent acrylic gessoes formulated specifically for encaustics. The reason is simply that wax, in and of itself, does not adhere well to other surfaces unless it can penetrate deeply into it and form a strong mechanical bond. While obviously encaustics are all the way on one end of the spectrum, adding wax to oils simply lowers its adhesion as well, not to mention increases brittleness, solvent sensitivity, and vulnerability to both cold and high heat,  The roughly 30% addition you mention would be at the furthest extreme limit of what would be advisable and we think you would be better using as little wax as possible if wanting to have the best adhesion.  If ultimately the desire to use wax is to have a waxy surface, you might consider forgoing it as an addition into the paint and using it instead as a final layer on top, to impart that type of sheen. 

    Lastly, if comfortable taking an approach of simulating the wax look using acrylics, that would make for a simpler process with far fewer potential issues and is something we have published about:

    Creating an Encaustic Look with Acrylics

    It should go without saying that sharing these articles are in no way meant to promote Golden's products. The approaches will work just as well with other companies, so take it in that spirit.

    Hope that helps to round out some of the thoughts already presented.

    Sarah Sands, Senior Technical Specialist, Golden Artist Colors
    2018-01-11 14:48:09
  • ApproveRejectUn-ApproveUser Comment

    ​​Thanks so much for these technical perspectives on my question, Brian and Sarah.

    2018-01-11 15:57:50

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