This problem just started happening and I would like to know what you guys think.
3 samples per pin pull are used, a regenerate grade nitric @ 68% is used with distilled H2O, 4 9s fine Ag is used and lead Assay cups. Mabor #7A Cupels are used and Coors #7 porcelain parting cup are used for parting and annealing. Cahn microbalances are used as well. ( Sample never leaves coors cup ) 3 to 27 samples are run at a time prior to this problem and now I'm just doing 3 at a time to try and resolve this. Here is my process. All our assays are in the range of 55% to 65% Au.
Cupels are placed in a 750c oven for about 15 min to rid moisture.
.5 grams Au sample + 1.5 grams fine Ag grain placed in assay cups.
Placed in 950c oven for 18/20 min--Remove and cover till cooled--nice clean dore!
Remove dore and brush clean--not rolled or hammered
Parting cups are placed on 168f hot plate with 1 part nitric 2 parts distilled h2O
Samples are placed in cups until reaction is finished.
Decant with distilled H2O
Cups filled with 2 parts nitric 1 part distilled H2O
When reaction is finished, decanted X2 with distilled H2O.
Dried on hot plate to remove H2O
Annealed in 750c oven and weighed.
I have done this day in and day out with great results but now I have this issue and have no idea where it came from or how to rid it. Looks to me like white salts??? as soon as the nitric hits the dore you can see it turning cloudy white. In order to solve this I made sure a ALL my supplies are new and from our same suppliers.
Thanks a lot,
Eric