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:
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.