After nitric acid wash. (Gold, Aqua Regia, Gold filled)

[SinisterGenuis]

Aah that had slipped my mind.
First, if there is mud after Nitric it can be metastannic acid.
The incineration will accomplish two things.
Convert the metastannic to Tin Oxide and then evaporate all Nitric so you don't create AR when adding HCl.

Sometimes the simplest of things deserve praise and to you my friend I give you that nod. I knew why I perform the steps as I do and as Harold stresses the importance of the HCI rinse so that Tin doesn't clog the later filtering process and create a labor intensive nightmare, but I had never seen it laid out so simply in a single sentence before. And As I progress with this current batch, and watch my solutions, I have no doubt it is packed with tin.