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  • Gamblin PVA SizeApproveRejectUn-ApproveSubscribeUn-Unsubscribe
    Question asked 2017-12-05 22:08:25 ... Most recent comment 2017-12-06 12:45:58
    Sizes and Adhesives
    Question

    In 2015 I contacted Gamblin asking for directions on a substitute product to RSG for sizing canvas.  The recommendation I received were instructions, developed by Robert Gamblin and Ross Merrill, former head of Conservation at the National Gallery, in point form.  After a few steps on how to glue canvas to a wood panel, Step 6:  Apply Gamblin PVA size to protect the surface of the canvas with one penetrating coat.

    I decided to purchase the PVA Size and after a few tests, and problems with the ground being too absorbent, I decided to apply 3 coats instead of 1, sanding and scraping before applying the last coat.

    On a Facebook forum I was informed that Gamblin PVA size had been tested by Sarah Sands (article dated 2013, Preparing a Canvas for Oil Painting | Just Paint,)  She tested the PVA size along with other products, and her findings showed that Gamblin PVA Size performed poorly, both in terms of flexibility and strikethrough.

    I am a bit puzzled by this:  Gamblin is providing me with instructions with big names undersigning them, plus "National Gallery" and the "Canadian Conservation Institute" are mentioned on the labels and online.   But then you have Sarah Sands, doing an honest test, showing that the Gamblin PVA size should not even have the name 'size' on it.  I am no expert, but I can read a chart.

    My question is, what is going on here? 

Answers and Comments
  • EditDeleteModerator Answer

    ​Hi -  

    My first and most immediate response was "whoa whoa - where you are getting that interpretation!". First, nowhere in the article do we mention Gamblin, and that is important as we do that on purpose and on principle as we would never directly comment on another manufacturer's products, especially in a way that might be construed negatively. When we use products from other companies we do so with an eye to simply understanding how they work with our own products, as we assume that people will mix and match out in the world and its important for us to be aware of those things. But we do not mean those tests to be evaluations of the products used within that manufacturer's own product line. We are not set up and it would be anathema to us to present our testing as a form of third-party consumer product testing for the industry. Finally, we also have great respect for Gamblin and have had a long relationship with Bob and would never imply that they made anything other than professional products.

    Second, here was our summary about PVA Size up near the start of the article:

    "PolyVinyl Acetate (PVA)

    While pH-neutral PVA adhesives have long been used in conservation and the book arts, some manufacturers now provide PVA-based sizes for use in preparing canvases. These should adequately protect fibers from the oxidizing effect of drying oils and prevent strikethrough. In our own testing, the number of required coats to achieve this was varied, with one coat clearly sufficient for a faster drying, alkyd-based ground we tested, while a minimum of two coats were required for all the slower drying, oil-based products. Always consult with the manufacturer and check for your own application to see what is optimal."

    Nowhere do we imply that a PVA Size is not a suitable and viable system. What we did find was that if paired with a fast drying alkyd-based ground, one coat was sufficient and worked well. It was with slower drying very traditionally formulated grounds, such as our own Titanium or Lead Oil Ground, where we saw strikethrough as the oil had days to be able to work its way down and through - and oil molecules are rascally things that are great at penetration, especially if given the time. A faster drying alkyd ground, on the other hand, sets up rapidly - often overnight - and so there is less chance of that happening. And even in the above case, applying 2 coats of the PVA size reduced strikethrough to a very minimal level, and I could easily imagine a 3rd coat would have taken care of that. But the main thing to keep in mind is that when pairing products, especially if choosing a size from one manufacturer and a ground from another, you need to do some testing to see what works as directions are almost always assuming the best process for use within a manufacturer's own system. So by all means pick and choose and combine, but when doing so you should assume that some adjustments to the instructions might be needed.

    Ultimately PVA Size is a well tested option that has a lot of use and acceptance in conservation circles and we think it is a perfectly fine option. The one we tested was quite flexible, especially if comparing to the absolute gold-standard for stiffening, rabbit skin glue, which is what we aim for duplicating when developing an option using our acrylic sizes. I am not sure, to be honest, if a PVA could be made stiffer, but I would not avoid using PVA Size on that basis alone if it is something you like using. It did leave the canvas feeling very supple - almost like it had no coating - and that has a certain allure.

    In the end I think you can feel that the Gamblin product is a professional one and I would not in the least disparage the company or feel that they in any way misrepresented it. They have had a long relationship with folks at the National Gallery - we share in the same contacts - and the Canadian Conservation Institute has done some of the most extensive testing of PVA Sizes around. They literally 'wrote the book' on the subject:

    https://www.iiconservation.org/node/877

    http://www.tandfonline.com/doi/abs/10.1179/2047058414Y.0000000129?scroll=top&needAccess=true&journalCode=ysic20

    https://pub.cci-icc.gc.ca/resources-ressources/publications/category-categorie-eng.aspx?id=20&thispubid=533

    and I would have no doubt that they reached out or worked with folks there when developing their product.

    Hope that helps give you some confidence. Pairing a size and ground and getting a system that is right for you can take some fiddling and testing. And never hesitate to reach out to Gamblin directly if you need assistance or have questions with their products. They should be very helpful based on my own interactions with them. And if you have questions about something we wrote - and in this case something I did - please reach out to us directly if needing clarification as well. We are always happy to do what we can.

    Thanks.

    Sarah Sands, Senior Technical Specialist, Golden Artist Colors
    2017-12-05 23:05:33
  • EditDeleteModerator Answer

    Hi again -

    Please link to my reply and share with the Facebook group you found this discussion as I would not want the misinterpretation to stand without comment there as well.

    Thanks.

    Sarah Sands, Senior Technical Specialist, Golden Artist Colors
    2017-12-05 23:13:51
  • ApproveRejectUn-ApproveUser Comment

    Hi Sarah, 

    I very much appreciate your reply and I want you to know that my intention for posting this question was none other than understanding.  

    I use a lot of products made by Gamblin, Golden and Williamsburg, and I am a very happy customer.  I trust what the technical support people recommend and say about their products. 

    I was not aware of your tests, and their interpretation is (from what I gather from your reply), not within my scope of competence.  But I have to believe what other experts say, so when I read this, and saw the chart, I made my conclusion:

    George O'Hanlon Group Admin You can use lead oil ground over a PVA size. One thing to note that studies by Golden Artists Colors demonstrated that PVA size may not provide adequate stiffness and oil blocking for the oil ground on canvas. With two coats it did not provide adequate oil blocking and stiffness. 

    2017-12-06 09:21:58
  • ApproveRejectUn-ApproveUser Comment

      

    2017-12-06 09:28:39
  • ApproveRejectUn-ApproveUser Comment

    Golden Size test results.jpg

    2017-12-06 09:32:00
  • ApproveRejectUn-ApproveUser Comment

    ​I am conducting my own test on the Gamblin PVA Size with the Williamsburg Lead Oil Ground on Claessen 13 linen canvas.  These are the products I have adopted in my practice.  My results may not be worth the paper they are written on, and will make no claim of any kind, other than at least I'll know 'for me.'

    2017-12-06 10:18:41
  • ApproveRejectUn-ApproveUser Comment

    ​Sarah I understand that the strikethrough occurs on a single coat of size, applied to a stretched linen canvas because of lack of protection to the back side of the canvas. So for instance, if the canvas is attached to a substrate, with PVA glue, one coat of size will be sufficient as the PVA glue is providing the protection to the back side of the canvas. Likewise, one coat of PVA size, applied to both sides of a stretched canvas, will isolate and protect the canvas from oil strikethroughs.

    2017-12-06 12:45:58
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