I never experienced the same things that Palladium and the others have. Everything always worked the same even though I'm sure I wasn't perfect enough to hit the nitric on the nuts each time.
To make a long story short, I think my success was mainly due to the dilutions. The 50/50 nitric was half water to start with and I always diluted it 50/50 again with distilled water before settling and filtering. After filtering, I put it back in the bucket and added the copper bars.
The same with aqua regia. I always diluted it 3 to 1 with tap water before filtering and I can't ever remember having any problems dropping the gold with a sulfite.
Another example. Awhile back, for about 4 months, I used stannous chloride at least 10 times every day. The gold bearing solution I tested was about 50% nitric. I put a drop of solution on a spot plate and added 1 drop of stannous chloride solution. It turned deep purple but the color disappeared in a second. I then tried adding 4 drops of tap water before the stannous chloride. The purple appeared and stayed for hours.
It's like diluting dulls the effects of the nitric considerably.
To make a long story short, I think my success was mainly due to the dilutions. The 50/50 nitric was half water to start with and I always diluted it 50/50 again with distilled water before settling and filtering. After filtering, I put it back in the bucket and added the copper bars.
The same with aqua regia. I always diluted it 3 to 1 with tap water before filtering and I can't ever remember having any problems dropping the gold with a sulfite.
Another example. Awhile back, for about 4 months, I used stannous chloride at least 10 times every day. The gold bearing solution I tested was about 50% nitric. I put a drop of solution on a spot plate and added 1 drop of stannous chloride solution. It turned deep purple but the color disappeared in a second. I then tried adding 4 drops of tap water before the stannous chloride. The purple appeared and stayed for hours.
It's like diluting dulls the effects of the nitric considerably.