Jessica As a commercial gold smith I normally use a boric acid
alcohol mixture to help prevent firescale. It is removed by the
normal pickling process (I use sodium bisulfate). IF this isn’t
cleaning your pieces of the coating, and sense you don’t have an
ultrasonic I would suggest using the older cleaning process of
boiling. Mix a soap/detergent solution and place in a pan suitable
for heating then bring the mixture with your items in it to a slow
boil. DO NOT ALLOW THIS TO BOIL DRY. Remove the items, inspect and
reapply until clean. Good luck.
When your finances allow consider buying a good ultrasonic unit, and
a steam cleaner. They are well worth the expense.
WayneM