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Hard investment


#1

I just came back from class in which I did my first casting. We had
problems tonight with the investment not cracking up easily and
coming out of the flasks easily. We had to dig out our pieces which
was a royal pain. Quite literally. My hands are still aching. So I’m
wondering what went wrong? It was a new container of investment,
just opened that night we did the investment (one week ago). We let
the flasks sit out maybe one minute after casting before dunking
them in water. How long should they sit before going into water? I
got the impression that they hurried up the wait time since the
first ones were not coming out well, and they thought that a quick
dunk would shock the investment to help crack it up. I’ve still got
a lot of picking to do to clean up those pieces even after getting
it out. What might have been an easier way to get it out? I was
thinking of something to dissolve the investment, but what? Vinegar?
Any help or insight is greatly appreciated.

Peggy K.


#2

When I cast with stone in place or let the investment set to long I
redehydrate it in the vacuum. Under water it all most pours out Don


#3

Peggy- What brand of investment was it? Some investments are really
hard.

Platinum investment comes to mind.

We use Ransom and Randolph investment. Kerr Satin Cast is another
great one to use as well.

We usually wait for several minutes, unless it’s rose gold, before
dunking in water and have no problem with the investment coming off.
A sonic and steamer helps.

Waiting a week before casting shouldn’t have caused this.

My suspicion is that it’s the kind of investment you used.

Have fun and make lots of jewelry.

-Jo
www.timothywgreen.com


#4

Don, how do you rehydrate the hard investment in the vacuum? Do you
put water in the flask and set it under the bell jar for invest?
Sorryif this is a stupid question, but I am not familiar with vacuum
rehydrating hard investment. Alma


#5
What brand of investment was it? Some investments are really
hard.'

We were using Satin Cast from Rio. Since this was a first time class,
and casting for me, I was casting in brass & copper. Same problem no
matter what metal anyone was using, even those using silver - we all
had trouble geting out the cast out of the flask. even those using
silver. There were several pours for the investment, one burnout for
all the flasks (I think). I’m so new to this, I don’t have much
ability to come up with a good hypothesis. But please do ask
questions. I can do some sleuthing and maybve come up with some
possible answers.

Peggy


#6

I’m most puzzled by these reports of hard to remove investment. I
have used both Gold Star Ultima and Kerr Satin Cast for my silver
castings. After I finish pouring I take the flask out of the vacuum
chamber ant leave it to rest on my bench on a heatproof slab. Usually
I’m busy at this point putting metal for the next melt into the
crucible and into the furnace. I then pick up the cooling flask and
watch the colour of the button which is usually a dull red at this
stage. I keep checking the button until I can see no glow when
holding the flask in the shaded area under the bench. As soon as it
has cooled to this point I plunge it into the quenching bucket. The
investment always breaks up beautifully as its heat boils the water.
When things have cooled sufficiently I retrieve the casting and clean
off most of the rest of the investment using an old toothbrush,
wooden chopstick and a satay skewer.

The only things that occurs to me is that you are letting the flasks
cool down to near room temperature before attempting to remove the
investment.

This is usually necessary when casting with stones in place, but a
waste of time and effort for a straight metal casting.

All the best
Jenifer Gow
Tears of the Moon Artisan Jewellery


#7

Yes I put the flask back in a bowl with water and vacuum again the
vacum pulls the air out when you release the vacum the water
reenters the investment. Don


#8

What is the flask temperature when you cast? Normal is 900F to
1000F, so a10 minute rest after casting should still be hot enough
that when you quench, water and steam evacuate most of the
investment in a boiling action.

Sessin Durgham
Rio Grande Technical support
Ext. 13837