Now that you precipitated your gold, it's time to rinse it. Your precipitated gold will be at least 99.95% pure. However, it is still wet with acid and the acid has dissolved copper and other impurities in it. So the gold must be rinsed clean of the acid and its dissolved impurities.
If you are refining material that has a high percentage of copper (such as e-scrap), then rinsing with water could precipitate copper hydroxide (a fine white powder) out of solution, contaminating your precipitated gold.
Ammonia doesn't precipitate copper hydroxide. After this first rinse there will be so little dissolved copper clinging to your precipitated gold that water rinses will not precipitate copper hydroxide.
If using ammonia: Add about a quart of water to your precipitated gold mud.
If using tap water: Add about a quart of water to your precipitated gold mud.
Stir and then the gold settle to the bottom of the container.
Carefully decant or filter the solution.
If you precipitated with sodium metabisulfite, save the solution to later recover lost gold.
This is a simple test, pretty much the same as the test for dissolved gold. Only this time you are testing the small amount of rinse water left behind after decanting in the second rinse, and this time you are testing for dissolved impurities.
Take a drop or two of the rinsed water left behind after decanting in the tap water rinse.
Put a drop of Ammonia Test Solution on top of those drops.
If you see any color change, no matter how faint, rinse again. Once it shows clean, go to Step 3: The final rinse.
Tap water has dissolved minerals. To avoid adding those minerals to your gold, do a final rinse with distilled water. About a pint of distilled water is all you need. For each rinse, if you precipitated with bisulfite, save the waste solution for later recovery of lost gold.