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Investment cracking


#1

Hi all,

I pour investment into the flask through a kitchen strainer. The
strainer prevents little clumps of improperly mixed investment to
enter the flask. If one of these clumps lays on the wax you will have a
casting that has a rough growth on the surface and investent imbedded
some where in the casting. Lines on the casting (bubble tracks) are
caused by investment that has too much water. You would think that if
a bubble leaves a track on the surface o f the wax the investment is
too thick. Not so. I speak from experience.

good luck
Lee


#2

NO, I did not just win that huge lottery.

The only thing I like less than casting, is recasting something that
should have come out right the first time.

I often cast and finish 1,000 pieces a week alone in my jewelry shop.

I also cast up to 300 lb single pour ceramic shell bronze molds.

I do not get investment cracking,porosity, inclusions, fire scale or
bad molds.

After 30 years of eyeballing it I learned how to follow directions.

I never have problems making molds due to rubber. I use Costaldo
rubber (pink) have spoken to Micheal Knight, a very knowledgeable
owner of a very good company. If you follow their directions exactly
everything works well, all the time.

I keep their wax injecting guide by my injector at all times. When I
have a problem a quick reference will fix the problem.

I use Ransom and Randolph Ultravest. I keep a stopwatch on my
investment bench and follow their directions to the second.

My water measurements are accurate, investment weighed to the gram.
If you mix investment for the recommended 3 minutes

not only will there be no lumps, but you will see it transform from a
gritty solid to a silky smooth liquid. I burn out for 6 six

hours and hold at casting temp for 1 hour.

These people spend as much time developing their products as we do
making jewelry. I’m all for experimenting,but our suppliers have
spent decades perfecting the use of these products, generally they
are more than happy to answer questions about them. If they say the
wax injects best at 1mm. thickness at 149 temp try it.

I have friends who judge the temperature of bronze by eye. Sure they
might be able to get to within 300 degrees.My used 40
year old $15.00 potentiometer can guess to within 3 degrees.

You may not want to take advice from a guy who reads directions
before assembling a grill or one that stops and asks directions when
lost.

However many of the processes we go through are not art but science.
There is a world of things out there to discover

Why waste time trying to figure out how to mix investment, or get
your rubber to vulcanize? Other people have all ready done that.

I know I’m not a better jeweler than the rest of you so maybe reading
and asking directions does help.

Or else I’m just the luckiest jeweler of all.

Sincerely Jeff Kahn


#3

Hi Jeff Kahn, I agree whole heartedly with your statement:

 However many of the processes we go through are not art but
science. 

As well as everything else you mentioned. For many years, I designed
jewelry equipment and was also a salesperson selling lost wax
supplies and machinery… That being said, I was also the guy that got
sent everywhere when customers would complain that their
wax/investment/castings where bad because of some supposed defect in a
material or machine. HAH ! Let me say that in hundreds of cases, it
was 99% Human error…or… faulty scales , faulty readouts on ovens
and controls,and people who actually believed that the bi metalic
temperature control on the side of a wax pot was "really " acurat e
!!! Investing was always the biggest call to go check out what was
going wrong… . In one year, 1 got 75 calls for investing problems…
1 call actually had a bad batch of material… It froze up 2 minutes
before schedule… sooooo adjust the schedule, or return the batch.
The batch was returned and since the manufacturer said to scrap it , I
inherited 5000 lbs of material that worked fine if you knew how to
adjust the mixing /investing schedule to make it work . All other
investment calls where due to people mixxing by “feel” or investin g
scales that were no longer accurate due to the internal spring
getting weak over time. also, Water temperatures . when the
thermometer had a slight bend or kink in it and it was actually 10-20
degrees out of wack !! Best thing to do is to follow directions and
make sure that all your equipment is accurate !

Daniel Grandi
We do casting and finishing in gold, silver, brass/bronze and pewter
as well as cnc model making for people in the trade.