I’m new to this forum and this is my first mail.I make jewells of
sterling silver and I would like to ask something that may seems
very simple to you but because I 'm from Greece the terminology you
are using
and is common between you is very unfamiliar to me.So to my
question: what exactly are you doing with your flasks after casting?
What I mean is that I do the following:
take the flask from casting machine (mine is centrifugal)
immidiatelly put the flask in a barrel of water where flask
separates from the tree+a lot of investment
we put tree+a lot of investment in a water machine where we
remove investment
we heat the tree with a torch and then we put it in
water+sulfiric acid (not boiling)
we repeat step 5 untill the tree becomes paper white After that we
cut off tree and compine the jewell parts then using 3 different
brushes we “smooth” the pieces and then we heat the pieces again with
the torch and put them again in sulfiric acid.The last step 3D is to
put them in a U shape polishing macine.
So I would like to ask is there a way to avoid the “mists” of
sulfiric acid but with the same result? Are there other methods to do
the same things? Are there any other order for doing the same things?
What a great job Greece did on the Olympic games…well done !
As for your silver casting procedures may I suggest that you NOT
plunge your casting into water until after it has cooled a
bit…most casting experts suggest that waiting for the sprue
button to cool to a dull cherry red is the best temperature for
de-investing.
As for the sulfuric acid fumes problem you might try to acquire some
sodium bi-sulfate as a pickeling solution. It is commonly available
as a swimming pool pH adjuster.
You add it to warm water until the solution is saturated and it
retains its effectiveness for a long period thereafter provided you
do not allow it to come in contact with iron or steel.The solution
should be kept warm for effectiveness. A copper container may be
used to contain the solution.Once it has become contaminated by
ferrous metals it is useless. You might make a set of copper tongs
to retreive items from the solution. You may also use your hands
without protection if you are tough skinned. Never allow the
solution to drip on anything with organic fibers as it will eat a
hole in them. Immediate rinsing in water will remove the solution
from your castings
Good luck !
Ron Mills,
Mills Gem Co.Los Osos, Ca. USA
Nikos, Fire scale, which is created when sterling is heated above
about 1000 degrees, is the oxide that shows up during normal
buffing as a dull purple of copper color haze on the silver.
The black oxide and fire scale starts to form immediately after the
pour. With centrifugal casting firescale is forming while the arm
is slowing to a stop.
The black oxide coating on a casting can be removed in a pickle
solution. Firescale is a little harder to remove or cover up.
Heating your silver pieces and quenching them in acid can cause
pure silver to move to the surface depending on how hot you heat
them. This process will cover the firescale. However buffing can
expose the firescale.
My anti firescale casting process prevents firescale from forming
when using the vacuum casting process. My process would not work as
well for centrifugal casting because of the time it takes to place
the flask into the reducing atmosphere.
Normally a flask should not be quenches for several minutes after
the metal is poured. The length of time from pour to quench will
depend on the weight of the metal and the bulk of the casting. More
metal and the heaver object require a longer time between pour and
quench. I normally do not quench until after 5 minutes after the
pour. In some cases, on very heavy objects, I will quench 15 to 17
minutes after pour.
Feel free to contact me off line if you still have questions.
I spent the first part of my jewelry career casting jewelry near the
Eastern Seaboard of the U.S. I spent the middle of my career
casting jewelry in Texas and I have spent the last 16 years casting
jewelry in Colorado.
Each of these places presented different results in the way my
casting came out due to the altitude and air quality. The higher
altitude of Colorado is ideal for casting.
My point is that only experimentation for your area is what is best.
I have never used the steps you are taking and I am inclined to ask
why you are taking this approach.
First I would ask what type of metal are you casting. Is it yellow
gold, white gold, sterling silver or Platinum? Each of these metals
would be handled in a different way with quenching after casting.
As for the steps of heating the tree and quenching in water, as a
general answer I would suggest that you at least wait until the red
color of heat is gone from the button. As for how long to wait again
depends on the metal that you are casting.
As for heating the tree and then placing it in water and sulfuric
acid. I would assume that this is your step to remove fire scale
and not the investment. If so there are safer non acid solutions on
the market. With this step you would actually heat the solution and
not the tree. If you are using this step to remove the balance of
the investment, you may want to try a high pressure water hose and
brush.
I am not quite sure why you are then cutting the tree apart and
heating and placing the parts in acid once again.
After Pickling the tree all that should be needed is to rinse the
tree cut it apart and do your pre finish work such as filling and
sanding.
After the tree is cut apart there are many methods to do the final
finish but for large scale operations a tumbler followed by hand
polish will give good results.
take the flask from casting machine (mine is centrifugal)
OK I’m with you this far
immidiatelly put the flask in a barrel of water where flask
separates from the tree+a lot of investment
I prefer to cool the castings for 10 to 30 minutes, depending on the
thickness of the pices or longer if we have caast with stones in
place, if we have then I put the flasks back in the oven and let
them cool down very slowly,
we put tree+a lot of investment in a water machine where we
remove investment
I use a hydro washer which is a water sprayer connected to an air
compressor gets off about 80 or 90percent of the investment.
we heat the tree with a torch and then we put it in
water+sulfiric acid (not boiling)
Not me, I cut my pieces free of the tree and put them in an
ultrasonic to remove the rest of the investment. then I put them in a
heated solution of Sodium Bisulfate (sp) or Sparex. which will remove
some fire scale, I also use a lot of anti oxidising casting grain,
(saves removing fire scale) then I remove any remaining sprue and
parting lines with a 3M gray wheel. the rest is pretty much the same.
only I tumble my pieces before I finish them in an abrasive media and
a short pre polish with stainless steel shot.