Wash your silver chloride well, until the wash water is clear, with no traces of color. You can do that with tap water. Make at least one of the washes with hot water, to dissolve any lead nitrate that might be present. If you make that wash the last, or second to last wash, you'll notice that the silver chloride will settle almost instantly, so you can decant while the solution is still hot. Lead nitrate will self precipitate when the solution cools, defeating the purpose for the hot wash.
I used a thick-walled Pyrex container for the conversion. There's enough heat generated that your chloride can achieve boiling temperature, so don't use glass that won't tolerate heat. Don't do this indoors unless you have a fume hood. There's a considerable amount of gas and vapor liberated in the process.
Place your chloride in the container, and cover it with a 10% solution of HCL and water (tap water is fine). A large diameter container with a shallow layer of chloride is best. You need room to stir. If you have access to scrap sheet aluminum, it works best, for it presents a large surface area to the chloride, and is easily recovered when the operation is complete. Smallish pieces that can be stirred work well, for you have to expose all of the chloride to the aluminum. Avoid tiny pieces that would be difficult to remove when the process is finished.
At first, the chloride will have a tendency to stick to the aluminum, but as it all converts to elemental silver, you'll find that the aluminum will shed it totally. The aluminum goes into solution in this process, so expect it to dissolve as it works. Make certain that the chloride has converted to gray (silver) and there's still some aluminum left. At that point the aluminum will bubble, being dissolved by the HCL, and will be very clean, but there is, otherwise, no action. When you're convinced the chloride has all been converted, remove the rest of the aluminum, checking any place that yields bubbles for small pieces that may be left behind. It's not a bad idea to add a little free HCL after you remove the aluminum, which will insure that the silver is well washed, and will expose any tiny pieces of aluminum that may be left behind. Allow things to sit for a few minutes. If there's any aluminum left behind, you'll see bubbles coming from the location. When you're sure you have all the aluminum, fill the container with tap water and allow it to settle. The solution will appear to be about the same color as the silver, and you'll swear there's silver in suspension, but that is not the case. Allow it to settle for a day, then decant the solution and repeat the wash. The wash will slowly come clear, but it takes a few repetitions. Once the solution is fairly clear, it will filter well, but the dark solution won't go through a filter worth a damn, so don't try filtering until you've washed the silver a few times.
My policy was to place the well washed silver in a Buchner funnel, where the balance of the solution could be removed and the silver compacted well for drying. It's a lot easier to handle the stuff after it's been compacted. I would then dump the Buchner contents into a large evaporating dish to force dry the silver over a low flame. The silver that comes from this conversion is very fine grained and sticky. It melts well once dry, but flux (borax, without soda ash) is a definite asset. The flux should be saved for future re-processing. It could contain traces of unconverted silver chloride, and possibly some prills. Soda ash would convert the chloride traces to elemental silver, but it would also convert traces of base metal oxides should they be present, so I avoided using it. All depends on your objective. If the silver is headed for a silver parting cell, the cleaner the silver, the longer the electrolyte will be viable. How you'll use the silver will determine how to flux. If you use it for inquartation, over and over, use some soda ash in your flux. You'll achieve a 100% recovery (of chlorides) that way.
Hope I've covered it well enough for you to proceed. It will take only one attempt at the process for all of this to make sense.
Harold
