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Dimple problem


#1

Hi,

I am a hobby jeweller and have been a silent lurker/reader for some
time and am learning constantly so I will take the opportunity now
to thank you all for that :slight_smile:

The query is that I used some melted down scrap, which I had rolled
out to make a brooch the other day. I textured it and all was going
fine until I soldered the catch fittings on to it and I noticed that
what I can ony describe as little dimples or bumps had occurred on
both sides of the brooch, in irregular spots.

They were easily filed away on the underneath but of course with the
texture on the other side it is not really possible. Can anyone tell
me what went wrong?

Thanks
Pam


#2

Sounds like your scrap had been contaminated. Maybe filings - iron -
solder on some of the scrap, some bezel material (that most
unlikely). And there is a difference between bumps and dimples - I’d
say dimples are depressions in the metal, and bumps are like little
mountains!

That is such a shame. Maybe that isn’t that best reasoning, but it
hits me right off the bat!

Rose Marie Christison


#3

When you melted down your scrap, and I assume you poured it into an
ingot mold, I would guess you had some air bubbles in the pour. They
will roll down fine but when you heat up to solder, these air pockets
expanded, giving you the dimples (Pimples?). The next time, preheat
your ingot mold to at least 500F. Make sure your pour is melted
completely and is totally fluid. Always do a test of the ingot by
heating up to just under the melting point to make sure you don’t
have any pockets before rolling.

Tom


#4

Hello Pam,

There was air trapped in the middle of the ingot, rolling it
flattened it but heating it caused it to expand.

Christian


#5
I noticed that what I can ony describe as little dimples or bumps
had occurred on both sides of the brooch, in irregular spots. 

This is caused by porosity in your ingot. When you roll such ingot,
cavities are elongated and become thinner and thinner. When you heat
such metal, air expands and creates these dimples. That type of
porosity is caused by incorrect temperature of the melt, and/or wrong
pouring speed. It could also be the result of metal contamination, or
improper flux used for melting.

Leonid Surpin
www.studioarete.com


#6

Wow, I learned something new! This is the greatest problem solving
group ever. I don’t melt and pour into an ingot…I was only thinking
as far as the melt was concerned when I commented on contamination. I
am happy to learn what you all said about porosity, the temp of the
ingot, etc. Thanks for enlightening me on the dimple problem.

Rose Marie Christison


#7

One other trick regarding the ingot, either melt some wax to coat it
or use a light oil after you heat the mold. The molten metal seems to
flow a lot smoother. Careful though, use sparingly in either case.
The oil will light off and spatter as the metal is poured into the
mold.

Regards, Tom


#8

Thanks so much to all of you who replied to my query. You are indeed
right - it was more a pimple than a dimple!!! I now know exactly what
to look out for and what to do to avoid it - so hopefully it will no
occur again. Thanks very much again for your willingness to help :slight_smile:

Pam