Casting at high altitudes

Jewelry Discussion
21

Back in the early 1970’s, my first boss in production casting,
Dominic Annetta of DoPaso Corp. in Albuquerque, developed an
investment formula that took all the bubbles out of the
investment. regardless of the altitude, brand of investment, size
of the pump, size of the bell jar, and so on. It is foolproof for
this specific purpose (bubbles) but also had some other very
desirable symptoms. Those other symptoms were smooth-as-silk
surfaces, detail like you have never seen before and hardness and
strength unmatched in other “room temp” formulas. A few times, we
accidently dropped 9" tall flasks on the cement floor while getting
them out of the oven. picked them up and plopped them into the
caster and cast them. There was no investment breakdown or missing
investment whatsoever. (Don’t try this at home. )

Dominic used 120 to 125F water to mix. The result, of course is
that the investment “boils” sooner. Thus, if you were in
Albuquerque at 5,000 feet and the end vacuum only read 26" on the
gauge, using the 120F water would cause the investment mix to boil
vigorously at between 20" to 23" of vacuum on the gauge. thus
allowing all the bubbles to be eliminated. Obviously, there are
some compensation factors that had to be considered. like set up
times that were 1/2 that of room temp investment and the
like. but Dom worked those into the formula. Using this hot water
formula. which I have used and taught to many in all the years
since then, and still use to this day, regardless of the altitude
where I happened to be, pump size, etc. one can easily
compensate for any deficiency in equipment or natural geography or
natural conditions that have heretofore hampered perfect investing. I
have just set up my lab here at my home in Idyllwild, Ca. , a full
6,350 feet above Palm Springs and I use a Busch 040 vacuum for my
casting chamber (break your hand over the opening-type of
pump). but for investing I use a pump so small and inefficient
that it couldn’t pull hot salt water taffy. But when I am done
investing. the bell jar is covered with so much investment
"splatter" I can’t even see inside of it. And the
bubbles?. what bubbles? My friend Doug Perry knows about
altitude from his perch high in the Rockies in Colorado, and his
answer yesterday is completely true and valid. But for those who
can’t afford a new system or to make drastic equipment changes, this
is the “other” answer. And as he also knows, this formula only
works for regular investing, not for platinum investments or my
signature product Doc Robinson’s Miracle Casting Plaster and
Elixir. the 3 hour wax to cast investment for platinum and
stone-in platinum casting. But it works on any brand of regular
casting investment. I really don’t know why GIA doesn’t know this
process intimately, as all during the 80’s when I was giving free
monthly seminars to GIA students and instructors at PMWest/Fine
Gold’s factory in LA, I was teaching this method. I can only guess
that the turnover in personnel after their move to the “Crystal
Cathedral” in Carlsbad was the reason noone now knows of it there.
(Except my friend Larry Lavitt, who was there then and is there
now. ) Anyone out there who would like this formula and all the
compensation factors can e-mail me and I would be glad to give it to
you. It is being used by companies from California to New
York. from the PRC and Hong Kong to Timbuktu. Or you can get it in
the archives of AJM Magazine from 1995 from the monthly column I
wrote that year under the title of “Curing Altitude Sickness” (4/95)

Thanks for the space. Marc “Doc” Robinson Goldbarz Consulting

goldmanic@tazland. net
(909) 659-4741

22

Hello, I live at 8000 ft in Co, and I don’t have much of a problem
with bubbles forming. I do spray my waxes with a soap solution, and
I make sure everything is in order for mixing the investment so I
don’t waste a second. I follow the instructions for the product
that I am using without going over on the time for any of the given
mixing times etc. I don’t use hot water and I don’t mix the
investment thinner. The mistake that I made when I first started
casting was trying to get the investment to boil but I would always
go over the time limit allowed for that step. It takes water longer
to boil at higher elevations. Now I just let it “perk”, for lack of
a better word, I don’t go over the time alloted for that step, and I
don’t have a bubble problem. For some reason I still find the whole
process nerve racking. Michael

23 
    Very good thinking (as always!) by John Burgess:  bubbles not
being left on the mold but forming there, as in a warming glass of
cold water--which reflects on the suggestion to use a warmer
investment, not to decrease the setup time, but to decrease bubble
formation. Bubbles don't form in a glass of hot water, do they? 

Air dissolved in the water is not the main source of air in the

mix. It is the air added by the mechanical mixing of the investment
and air trapped in the powder. To prove this you can de-gas the
water by putting it under the vacuum bell jar for a few minutes
this will de-gas it just like boiling it. Then use the de-gased
water to mix your investment you will still have air bubbles.

The hot water use of hot water makes the investment thinner, that

is the reason for doing it not to speed the setup time. You really
don’t want the setup time speeded up that is why some people use the
citric acid to slow down the setup time. If you are only filling a
couple of flasks then the faster setup time is not really an issue
however try filling and vacuuming six 4x9 flasks with a 4.5 minute
setup time, you may not make it. There is another benefit of hot
water investing, the investment is stronger so if you have problems
with investment breaking you might also try this.

Jim