Thank you all for the help. After talking with Bostick & Sullivan we are going to try ammonium dichromate or potassium dichromate (see pages 222 and 223 in C. James). We have both dichromates in our classroom inventory. If that fails to get to reasonable contrast I will be the happy new owner of 250 grams of ferric citrate from http://www.sigmaaldrich.com/catalog/...g=en&region=US.

John