When Jeffrey Mathias tested various batches of ferric oxalate in the 1990s he found that the B&S ferric oxalate was about 89-91% pure, the Artcraft FO 95% pure. See http://home.att.net/%7Ejeffrey.d.mat...e/contents.htm and in Chapter 6 click on Formulas for FO Sensitizer Solutions.
This information may or may not pertain to current supplies. However, I obtain my FO from Artcraft and can state for a fact that in my work it has always been of consistently high quality.
Originally Posted by Kerik