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Porosity


#1

Hi, I casted 5 rings and 1 pendant yesterday and I have 2 problems -
both are which K14 peach gold. For the ring, I used the 'porcupine’
method (cf. Doug Zaruba), sticking wires (1.5, 2 and 3 mm thick) of
Sterling into the wax. After the casting, it turned out that some of
the sterling wires had holes in them. The porosity (if that what it
is) was so deep that it went all the way trough. Also, I used sticky
wax on the outside of the ring to make sure that the wires would stay
into place. This was probably a bad idea (and illogical too, but I
got paranoid). It turns out that the result on the inside of the ring
is better than on the outside because, after filing away the gold
(where the sticky wax wax), on two occasions the silver comes not
through anymore - it just isn’t there. My guess is that the flask was
still too hot and maybe the diameter of the wires is too small. Does
someone has ideas or tips concerning the right temperature. The second
problem is about a pendant (peach K14 gold, 15 grams). The pendant
has a deep hole on the back (almost 2 mm diameter) with a ugly black
color that doesn’t not seem to be removable. I am planning to fill
the hole with solder, but the black substance worries me as I am
afraid that it will prevent the solder to stick to the piece.
Pickling the piece does not help. Does anyone has a suggestion? How
can I prevent these things from happening. Thank you very much for reading.
Best, Will (a bit in despair)


#2

Sounds like quite a mess—Nobody can say what it is you
have without actually looking at it. I have two thoughts, though.
The recommended burnout temp. is 1350f., by the way. I’ve never done
the silver wire thing you describe, but the thinner the silver, and
the hotter the flask (and thus the SS wires) at the time you cast,
the more instantaneously they will dissolve in molten gold. And make
sure you soak it good, so the core is the same temp. More
importantly, though-- If you have cracks/seams where wax meets wax,
or if you have small holes and the like, such as if you drilled the
wax with pilot holes, then you have tiny pieces or flakes or rods of
investment, after the wax burns away. Investment WILL go inside of
incomplete (un-fused) seams of waxwork. Then, when the heavy mass of
metal (very much especially platinum), comes roaring through, it
breaks off those tiny pieces, and becomes just the sort of porosity
you describe: Giant holes with crud inside of them, usually impossible to fix…


#3

Hi Will, The casting term for what I understand as Doug Zaruba’s
"porcupine"method is called a “chill”. Sometimes a small bit of
heavy fishing line attached with some wax or crazy glue will work
quite well. I use a “chill” only when a sprue of proper size cannot
be used because of texture or design. A chill is supposed to set up
the recrystalization of the casting quicker in the location of a hot
spot. I regularly cast very unique wax carvings that sometimes have
up to 5 “Hot Spots”. If you don’t feed a casting with sprues slightly
larger than the thickness of each “hot Spot”, you are courting
porosity. After spruing to each of the hot spot the sprues should
gather to one spot and attach to a trunk slightly larger than the
sum of all the sprues, there should be a button on the base of the
trunk. So you see that we’re looking at a total casting system that
can be up to 4 times heavier than the piece being cast. Whether a
casting has 1,2 or more hot spots, it is important to locate them and
give them the feed they need. 90% of porosity is due to poor spruing.
Contamination and overheating make up most of the balance of the
other 10%. On your black hole problem…try using some muriatic acid
from the hardware store, full strength, with plenty of active
ventilation. John, J.A.Henkel Co., Inc., Moldmaking Casting
Finishing, Producing Solutions For Jewelry Artists


#4
Giant holes with crud inside of them, usually impossible to
fix..... 

Well yes and no. If I have worked to make a one of a kind wax and
then find a problem after casting, like a hole (with or without the
crud), I would be unhappy to have to throw it into the scrap box and
start over again. Rather, it is often possible to drill out the hole
(and crud) make a piece of wire the exact diameter, fit it into the
hole and solder in place. If done carefully, it cannot be seen!

Cheers from Don at The Charles Belle Studio in SOFL where simple
elegance IS fine jewelry! @coralnut1


#5

Hello John,

Thank you for your answer to my message.

John, I am sure that you are right about the cracks. The other day,
I made a band and when done, I drilled a hole in it and carved it
out, so as to put a tube in it. Once the tube fitted, I welded the
two pieces together with a speedy wax pen and, to make sure that
everything was okay, I strengthened (so I thought) the seam with
sticky wax. I am sure that there were no holes. Still, after the
casting, I had the same phenomenon again. I think that the seam was
not fused altogether. That is causing the problem. It is strange to
see how the investment goes into the tiniest seams. Well I learned
this the hard way. Let’s make seams that are fused absolutely well
next time.

Thank you and best regards,
Will