</span><table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td>QUOTE (Robert Kennedy @ Feb 3 2003, 12:41 PM)</td></tr><tr><td id='QUOTE'>Now, I have seen two formulas out there.&nbsp; An "classic" forumla known as "A" and another formula called "B".

So what is the difference?</td></tr></table><span class='postcolor'>
The classic formula calls for a stock solution A of ferric ammonium citrate, and a stock B solution of potassium ferricyanide, you mix them 1:1 before coating your paper.

In addition, there are many versions of the formula. There are other formulas that add oxalic acid to both, as well as ammonium dichromate to solution B, others.