David,
We used to use a lot of solder flushed colored golds for overlays on
belt buckles.
Of course it is available - but you have to purchase a "mill run"
from one of the refineries… We couldn’t always find enough guys to
split the quantity into manageable amounts for each of us.
So, what we usually had to do was what you are doing - but with one
added step. After speading the solder on the sheet as best we could
with a torch, we would put it in the oven to even it out. Those
"lumps" you wrote about can be a real problem when they show up as
air pockets underneath your overlay. It always happens way out in the
middle of the overlay… Murphys’ Law. Pickle it and put fresh flux
on it before you put it in the furnace. Then pickle it again after it
comes out of the oven, and before you start using it.
One other trick: coat the upper side with boric acid, let it dry -
very lightly spray it with an antiflux before putting it in the oven.
Sometimes it would run over or “eat” the edge a bit, if there was too
much flux. Watch your temperature, you can also ruin the sheet while
flushing it or while soldering it - if you allow it to get too
high…
Brian P. Marshall
Stockton Jewelry Arts School