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Shakudo, water casting


#1

While pouring a 50 gm ingot of 5% gold and 95% copper through
water into a canvas support , which i have successfully done
many times i experienced an exposion as the metal hit the water.
The result was no injury though a significant rise in the heart
rate. The metal appearred to disintergrate leaving a fine dust
all about the hearth. Having gone over the cast the only factors
that could have been a cause that were different from earlier
casts were a. a contamination of the alloy. b. a change in pouring
temperature lower than the first two pours of the day I continued
to pour more ingots having carefully cleaned the area and using a
new crucible and the work continued without incident. I am keen
to get to the cause of this incident. Any ideas or similar
experiences that might assist. Thanks David


#2

Hi David, Hmmm. I wonder if there was an air bubble of some size
under the canvas sling? That bubble of air, if big enough, would
heat up and force up the sling-full of metal in a big hurry. I
had this blow-out thing happen to me once when poring 20g of fine
silver: In my case the sling was supported by a open-bottomed
tincan (a biggish can) but I hadn’t cut any ‘legs’ on the bottom
of the can. I think the legs would’ve helped reduce the blow-out
effect of any air-bubble there, as there would be an escape
route between the legs.

    The result was no injury though a significant rise in the
heart rate. The metal appearred to disintergrate leaving a fine
dust all about the hearth. Having gone over the cast the only
factors that could have been a cause that were different from
earlier casts were 

Also in my case the blow-out resulted in no injury - the metal
was cooled by the water immediately it blew apart into little
droplets on the ceiling etc. Quite a shock, though.

    a. a contamination of the alloy. 

What do you mean by this? What contamination and what might it
have done to the pour?

    b. a change in pouring temperature lower than the first two
pours of the day 

What is your usual way to gauge the temperature of the melt at
pour?

Brian

B r i a n A d a m J e w e l l e r y E y e w e a r
@Brian_Adam1 ph/fx +64 9 817 6816 NEW ZEALAND
http://www.adam.co.nz/ 1 hour ring-making sessions