In a number of places you recommend DTM Bonding Primer by Sherwin Williams as a ground, particularly for use with aluminium panels.
The EDS data sheet suggests it contains zinc.
Zinc (as Zn) 2% by weight
Zinc Compound 3% by weight.
https://www.paintdocs.com/docs/webPDF.jsp?SITEID=SWPCGPROT&doctype=EDS&prodno=035777281734&lang=2
In dry form the percentage of zinc will be much higher.
Yet elsewhere you frequently warn to check for zinc content. For example in your Grounds and Primers technical resources state: ‘Zinc white has been found to react with components in oils and alkyds and form “metal soaps,” which in turn can give rise to delamination, wrinkling, the formation of white-colored aggregates, and the softening of ground/paint layers. Research is presently being carried out to determine the extent of damage that can occur when these materials are present.’
Can you please clarify? Is the zinc in a different form or are there other reasons why this product is suitable despite the presence of zinc? Have I misread the EDS – I’m not a chemist! There are a number of people on my forum (Wetcanvas) discussing this and we are interested in the clarification.
Thanks Brian, very helpful distinction. I wonder whether that distinction might be worth an edit to your technical guide when that is due because many artists are seeking to eliminate zinc in all its forms due to lack of clarity on this topic.
And apologies – after I posted this I used your search facility to find my question on the forum to check for response and it didn’t show up. Thinking it failed to post I repeated it. Please feel free to delete the duplicate.
This is very helpful and instructive. I’d like to push a little further for clarification.
1. “Zinc oxide has only been shown to be problematic bound in drying oils, not acrylic dispersions/emulsions like the one used in the SW product.” Can you please clarify whether: a) Considered safe: Zinc within acrylics is considered suitable for use and conservation purposes based on chemical theory and/or evidence; or b) Considered inconclusive: No significant problems have been detected but there is insufficient research to draw conclusions.
2. “DTM Bonding Primer by Sherwin Williams has been tested and found to be a suitable primer for ACM” (from an older question.) In tracing back I found the source of the testing referred to in several answers was this article: https://justpaint.org/painting-on-dibond/ The rationale for ‘testing’ of four selected products was confined to their suitability for use on Dibond as a primer. The author did not examine ingredients or ask questions about conservation, such as aging properties/ brittleness, cracking, delamination over time… Obviously in this case it would need to be based on what is known about ingredients, additives, etc. My question: where conservation is a strong consideration – is there sufficient evidence-based rationale to use these newer products?
Zinc oxide has only been shown to be problematic bound in drying oils, not acrylic dispersions/emulsions like the one used in the SW product.
One thing to note is that the datasheet does not specify the zinc compound. We cannot assume it refers to zinc oxide. Onnly zinc oxide is known to form zinc soaps that pose problems in oil paint.
Thank you, George, I was thinking the same thing but was not confident enough to post as a verified fact.
