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Working on a porous casting

#1

I’ve never had a problem with the people who do my casting, but my
last batch of small items seem to be quite porous. When i try to
solder small findings the solder is immediately absorbed into the
cast piece. After awhile there seems to be enough solder on the
surface, but the piece is so hot that the findings melt. What is the
best way to handle this? (I don’t want them to be done over.) I
thought it might be sensible to prepare the piece by melting hard
solder on it to sort of fill it up, then solder the findings with
medium or easy solder. I don’t know if that will work, or if it is
the best way to go about it. I would really appreciate any advice,
ideas etc.

Sandra
www.elegantinsects.com

#2

Have you tried burnishing the surfaces? A rotary burnisher is good
for closing poreosity. I use the laser for this now, but still find
my assortment of burnishers very handy, sometimes even after the
laser.

#3

if it’s so porous, have you tried contacting your caster? perhaps
you need to talk to them about redoing a bad job? You’re paying for
quality results and you didn’t get them. Such results can come from a
few things, but one common thing would be using too much “old” metal
when they cast, and considering the current costs of metals, I
wouldn’t be surprised if some casters are tempted to use more scrap
than they would usually would(you should never use more than 50%
‘old’ metal, and that needs to be pretty clean as far as solder etc).

If you do need to fill a hole in a casting, what I have found is that
you can drill out the hole and clean it up. Then take a small ball of
silver (melt a small piece of scrap) and some solder and place it in
the hole and heat it until the solder flows in and around the
ball… then file it down again. This only works with larger holes.
With some of my castings, I get internal air bubbles in the wax that
become holes when I cast. I don’t always see them before it’s cast,
so that is how I fix it. When I try to use just solder, it doesn’t
flow into the hole properly. But if your piece is porous in general,
I’d complain to your caster.

Jeanne