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Question asked 2018-10-31 23:25:40 ...
Most recent comment 2018-10-31 23:23:00
Are there likely to be similar issues with PW7 in oil as there is with PW4?
Answers and Comments
It is our opinion that any zinc-containing pigments may pose a risk to the integrity and future preservation of a paint film.
I wanted to amend my above statement a bit. After some discussions with Sarah Sands at Golden Artists' Colors, she has brought some very good points to my attention: zinc sulphide is used in lithopone (more technically , currently a cobalt-doped version of zinc sulphide) which was and is an extensively used pigment in coatings for over a century with no evidence that I have ever been able to find linking its use to soap formation or brittleness. Considering how extensive it was used in commercial coatings up to the 20s - it was the #1 white pigment between lead's demise at the turn of the century and titanium's rise some decades later - and the fact that the commercial literature quickly and rapidly noted issues with zinc oxide, it seems strange that issues with zinc sulphide are largely completely absent in commercial journals and reports. Well, beyond UV darkening which the cobalt-doping and better production took care of. We fear that zinc sulphide is unduly being associated with issues posed by zinc oxide, while everything we know chemically points to the sulfide form of zinc (unlike the oxide one) is inert and non-reactive. People will find zinc sulphide in basically all modern cadmium yellow and oranges, where it can occur in percentages as high as 25%. Also it would be very useful to reference a previous thread which can be found here.
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