I didn't usually inquart or evaporate down or use urea or incinerate. I used dedicated plastic buckets to drop the gold in and never had problems losing gold in the scratches
I dissolved everything I could (all the Ag, Cu, etc., in 10K, or less) with very hot 50/50 nitric. I then rinsed the residue a bit and used aqua regia, with a bare minimum of nitric. After dissolving the gold, I diluted the AR at room temp, with 3 times its volume of tap water and added a little sulfuric, especially when I had class rings. I let it settle fairly well, siphoned or decanted off the tops, filtered the tops completely and then the residue on the same filter. I rinsed the residue several times with hot water and then added a warm solution of sodium sulfite to drop the gold. I filtered and rinsed the gold with hot tap water (about 5 times). All done in the same filter, I then leached with ammonia, rinsed 5 more times, leached with about 25% nitric, rinsed 5 times, and rinsed twice with hot distilled water. All this rinsing and leaching took about 30 minutes - good gold powder filters fast. I always had vacuum filters, of various sizes, but I preferred a fairly big plastic funnel sitting in a hole in a piece of plywood over a bucket. I had about 10 of these going all the time.
The residue was treated separately - I sometimes removed the AgCl with ammonia and inquarted the gold chunks left over, when I got a bunch of them. Usually, about 96-97%, or more, of the gold dissolved in the AR - sometimes, all of it.
In general, the lower karat gold has a larger percentage of silver than the higher karats. I got rid of it in the 10K (the worst) with the nitric. Most of the 14K, 18K, and 22K breaks down completely in the AR.
I never had trouble with silver. It was always copper. If any was present, I usually could remove it in the melt. It's a guess, but I think I only had to re-refine about 1 out of every 20 batches.
The best heating source I've ever had was a 6' gas restaurant grill. You could keep it hot on one end and warm on the other, with a whole range of temps in between. You could cushion it with a cloth made from the material used for furnace gloves. We used to use asbestos cloth.
With 10, 4 liter beakers, I could do several hundred oz/day.