In order to achieve accuracy and consistency, it is important to begin with an accurately formulated sensitizer to which the metal solution will be balanced.
 

Summaries of Various Studies

The Comparison of FO Powders Study provided estimates for the concentration of Ferric Oxalate (FO) in FO Powders.

 

FO Powder	% ferric oxalate by weight, estimated	% oxalic acid or other material by weight, estimated
Bostic & Sullivan	89.2	10.8
Vizcay	98.08	1.92

The Verification of FO Powder Composition study used the work of Dick Stevens to relate the percent concentration of Ferric Oxalate in a solution with its specific gravity.  It was found that the Stevens' model and specific gravity information do not accurately relate to the concentration of Ferric Oxalate.
 

The study of the Threshold for FO Solutions determined an optimized sensitizer solution as having 26% ferric oxalate when optimally coated onto Cranes Parchment paper (CP).  The slightly higher concentration of 27% may be suitable for most papers providing a margin.  Further threshold study resulted in optimized sensitizer solutions and estimated purities as follows.

• 24% for Ultra pure Vizcay powder FO - 98% pure
• 25% for Artcraft powder FO - 95% pure
• 26% for Bostic and Sullivan powder FO - 89% pure

The study of the Oxalic Acid Concentration in the FO Sensitizer determined a benefit of having Oxalic Acid in the sensitizer solution at a concentration between 2% and 5%.
 

The Clearing Study resulted in a recommendation for the addition of 0.5% EDTA (CAS: 60-00-4) and 3% Oxalic Acid to the sensitizer solution to facilitate efficient clearing.
 

To determine the formula for a FO based sensitizer solution, use the Sensitizer Formula Calculator (requires a JavaScript capable browser)