When testing investments and casting samples in the Kerr refractories
QC lab, we measured the water – but we used only distilled water.
Thereare variations galore in most municipal or well-water systems.
Blessed be…
Where I’m from it’s either well water or rust filled city water…
so from the beginning we always used DI water to mix our investment.
Keeps the water variable constant.
MAK
we always used DI water to mix our investment.
Really? Surely distilled would be fine-- and a lot cheaper!
This was originally my post, so I’ll mention that on Monday I’ll see
the results of the casting we put together on Friday (the boss takes
it home to burn out & cast). We weighed the water… and it finally
came to light (after many statements by our wax person that she
always follows the written procedures strictly) that, well, she does
always add just a little extra water… Gee, do you think that
matters?
Hah! So now we won’t really know whether weighing made the difference
(if there is no spalling this time), or just actually going with the
measured amounts without throwing in that extra tidbit “just to give
a bit more working time”.
Noel
We weighed the water... and it finally came to light (after many statements by our wax person that she always follows the written procedures strictly) that, well, she d= oes always add just a little extra water... Gee, do you think that matters?
A small amount of “extra” water would not matter depending on what
“extra” means. I have found that small amounts of investment, for
about 2 1/2" x 4" flask will set faster than a 3" x 6".
When I talked with Noel, we discussed water temperature. I use room
temperature, but I have used cold, and in the winter, Denver, Co.
water is cold.
My opinion is that when you measure by volume, you cannot be
accurate, you will add a little more, or less. I believe if you
weight the same amount 3 times by volume, you would have 3 different
amounts by weight. My last post did not make it through. I mix for 1
1/2 minutes, vacuum mixing bowl for 1 1/2 minutes, vacuum flask for
1 1/2 minutes. I have done this for many years with success.
Richard Hart G.G.
Denver, Co.
We weighed the water... and it finally came to light (after many statements by our wax person that she always follows the written procedures strictly) that, well, she does always add just a little extra water... Gee, do you think that matters?
If your investment is too wet your casting will be porous. It’s
always best to follow the directions exactly. I use Satin Cast, and
while the investment looks too thick, it actually makes perfect
castings.
we always used DI water to mix our investment. Really? Surely distilled would be fine-- and a lot cheaper!
Usually, deionized water is cheaper to produce than distilled. Unless
you’re using large quantities, the easiest source for either is the
grocery store, where the price is usually the same for either. OTOH,
you can distill water yourself, for only the energy cost (which could
be significant) and an initial investment for the still.
Al Balmer
Pine City, NY
We weighed the water... and it finally came to light (after many statements by our wax person that she always follows the written procedures strictly) that, well, she does always add just a little extra water... Gee, do you think that matters?
A small amount of “extra” water would not matter depending on what
“extra” means. I have found that small amounts of investment, for
about 2 1/2" x 4" flask will set faster than the amount for a 3" x
6"flask. I have forgotten to tare my triple beam scale for the
weight of the measuring cylinder and mixed with less water than I
should have used, threw in some extra and everything was okay. I had
heard that investment should be the consistency of sour cream, my
opinion is that it is the consistency of sour cream that has been
stirred up, not as it is when you open it.
When I talked with Noel, we discussed water temperature. I use room
temperature, but I have used cold, and in the winter, Denver, Co.
water is cold.
My opinion is that when you measure by volume, you cannot be
accurate, you will add a little more, or less. I believe if you
weight the same amount 3 times by volume, you would have 3 different
amounts by weight. There is also an assumption that the measuring
cylinder is accurate. My last post did not make it through. I mix
for 1 1/2 minutes, vacuum mixing bowl for 1 1/2 minutes, vacuum flask
for 1 1/2 minutes. I have done this for many years with success.
Richard Hart G.G.
Denver, Co.
always follows the written procedures strictly) that, well, she does always add just a little extra water... Gee, do you think that matters?
That little bit of extra water - by itself - probably won’t be
enough to cause spalling, but it can be a force multiplier. As I
tried to say in my first post, it’s usually a combination of small
errors that cause things like spalling. As Richard pointed out, you
can get by with a little extra water, or water that’s too cold, but
put the two together with cold investment and the working time will
definitely extend. How much and what the result will be depends, but
I’ll bet in a situation in which both are 20 degrees too cold and 5%
too much water is used, the gloss-off time will be pushed out to at
least 12 or 13 minutes. That’s enough to cause the water marking
especially if the working time isn’t extended to compensate.
Fortunately, this is easy to check, just mix a batch and work it as
usual and actually time it all the way to gloss-off. If it’s around
11 to 11 1/2 minutes, you’re fine, the problems are probably
elsewhere. If it’s a little longer, extend the working time a little
to adjust the time from topping to gloss-off so it is two minutes
flat. If it takes 12 minutes or more, check every step to find out
why and try to fix that. This is for Kerr Satin Cast 20, other
investments are different, some substantially.
I was given the same advice by Ransom and Randolph to weigh the
water, but it was in the context of the cheap plastic graduated
cylinder I got with the casting equipment. Turns out it was way off
and that was the cause of the problems I was having at the time. The
temperature problems I had later were due solely to the change of the
season. Turns out that the concrete floor I stored investment on was
getting pretty cold, as was the tap water I was using (northern New
Hampshire in November, don’tcha know). The fix was to put a pallet
under the box of investment and keep water in a jug for use at room
temperature.
My experience is that spalling is more commonly caused by burn-out
issues. The flasks really need to sit absolutely undisturbed (even
vibration through the floor from a polisher or vent fan nearby can
create problems) for at least two hours after gloss-off before
starting the burnout. The temperature really should stabilize at
around 350, 700 and 1300 for at least an hour each, with two hours or
longer being better at the top. The rate of climb really needs to be
pretty gentle too, I use 2.5 degrees per minute max, 2.0 for the 700
to 1300 climb. This can all be done manually, but an oven controller
makes it a snap and takes all the guesswork out of it.
The reason for the long pauses at the different temperature levels
is the same reason that your favorite beverage doesn’t get cold the
second you put it in the fridge. It takes a while for the ambient
temperature to soak into the bottles or cans (OK, not technically a
correct explanation, but you get the point). Same thing with your
flasks. Another factor is the size and number of flasks. Three cans
of soda will cool off pretty quickly, but three gallons of spring
water can take a while to cool thirty or forty degrees.
The reason for the slow climb to temperature is that when the
temperature is raised say 600 degrees in one hour (700 to 1300),
that’s a rate of climb of 10 degrees a minute (600/60). The
temperature difference between the steel of the flask and the core of
the investment at that rate can be a hundred degrees or more, and
that can have the same effect as quenching a hot sapphire. Just like
sapphire, the investment can’t handle that great of an
external/internal temperature differential and can react in a
similar manner, especially if it is already a little on the weakened
side from not being properly measured and mixed. The
temperature-induced shattering of the investment appears in the
castings as spalling and the fragments can range in size from dust to
full-blown chunks.
I’m not normally one to advise following instructions (just ask Mr.
Ramsey, my high school vice principal and chemistry prof, the first
person - but certainly not the last - to thoroughly, accurately and
officially document my propensity for disregarding formal
instruction), but the folks that make that stuff know what they are
making it out of and how to use it for best results.
The bottom line advice I would give to begin troubleshooting is to
follow the investment manufacturer’s instructions to the letter, from
first scoop to throwing metal, including their recommendations as to
temperature of water and investment. If they didn’t consider every
variable to which they assign a number or a time to be at least a
slightly important detail, they wouldn’t have bothered to figure it
out, write it down and print it out so we can get excellent results
and buy more of their investment.
For every step that I’ve said is important, someone will almost
certainly be able to say they’ve been doing it differently for forty
years and never had a problem. That’s great and I won’t argue their
success (sure wish I could say the same about anything though -
especially casting), but if you’re having problems, I’d still try it
exactly the way the guys that made the investment tell you to before
trying anything else.
Don’t be too shy Noel. My guess is that they hired you to help
figure things out as well as for the skills you already have. Getting
nice castings consistently will save them a lot of money over time.
It’ll make your life easier and more productive too. Those are good
things that a good employer would want you to pursue. If they don’t
want to hear what you have to say, maybe, well, you know where I’m
goin’ with that.
Best of luck!
Dave Phelps
TLDR: You can probably get away with small investing errors, as
long as the burn-out is right. You can probably get away with a
slightly too-quick burn-out as long as the investing was done right.
You likely won’t be able to get away with both. In case of trouble,
follow the instructions exactly before trying anything else. If your
boss is a jerk, well… you know what to do. -DP
Also remember that your dehumidifier produces distilled water. All
you have to do is collect it. It might take a while to gather
enough, but over time the dehumidifier produces gallons of the
stuff.
John
always follows the written procedures strictly) that, well, she does always add just a little extra water... Gee, do you think that matters?
I was actually being sarcastic when I wrote this-- expressing the
apparent attitude of the wax person.
The first casting in which we weighed the water came out exactly
like the other castings-- plenty of spalling and porosity. The flasks
sat for at least a couple of hours before going in the burnout,
because they were here at work at least that long before the boss
took them. The flasks were small, with only a couple of items each,
so heat differential inside and out should not have been an issue.
The sprues look big enough to me, but maybe we’ll increase them
anyway, since it’s about the only other thing I control.
Here’s another clue, though. A couple of the buttons came out lacy
around the edges. Does that mean the boss is overheating the gold? If
so, would that cause spalling or porosity?
I really appreciate the help with this. I am very bothered by the
problems with our castings, even if the boss is not.
Noel
Great post. What a break to have Orchid to learn from as I start my
Casting and Plating career. I have already learned so much by reading
the casting threads in the archives, and have gotten some pretty good
results with my first 5 or 6 casts. I have a lot of questions myself,
but will pace them so they don’t get too tedious. For now, can
someone explain what “gloss off” is. I now understand from Dave’s
post that it happens when the investment starts to set, but what does
it look like? What are the important characteristics of “gloss off”?
Thanks to all the experts for being so generous with their time and
knowledge.
Jim Newton
How old is your investment? Do keep it from absorbing moisture from
the atmosphere? Try another batch of materiel, see if that helps.
Hi Noel,
I really appreciate the help with this. I am very bothered by the problems with our castings, even if the boss is not.
I guess at this point, I would wonder if this is something that is
just done this way and your employer does not mind how the castings
come out. She is seeing them first, and if she does not question the
quality, it ain’t an issue, just fix them, that’s what you are
getting paid to do. Would not be a process I would be please to be
involved in, condolences if that is the case. It is hard to over
heat gold or silver. I have a huge oxy-acetylene torch, rose bud tip,
I can cast 10 grams, or 350 grams with it, porosity is rare. I get
the metal hot fast, once molten, add borax, I shake the crucible back
and forth (centrifugal casting) till the surface is shiny, and let it
rip.
Richard Hart G.G.
Denver, Co.
For now, can someone explain what "gloss off" is.
I have fluorescent ceiling lights with grated covers on them in my
casting room. I look at their reflection on top of the flask. After
the investing sequence is finished and the flasks are setting until
gloss-off, the investment looks smooth and shiny. It starts to get a
little lumpy looking as it gets close to gloss-off. Gloss off occurs
when the first spot loses it’s shine, in my case, it’s when the grid
starts to be impossible to make out somewhere. The instant I can’t
make out the ceiling grid in the entire reflection is when I punch
the button on the clock to stop timing.
Casting is three parts science, two parts art and one part PFM (Pure
F… er, uh… Magic - same thing that makes helicopters able to fly
at night). One of these days hopefully I’ll be able to figure out
which parts do what.
Hope this helps James!
Hi Noel,
A couple things jumped out at me in your last post. First, the boss
is taking the flasks home (or somewhere else) for burn-out and
casting. That’s fine if he’s treating them like un-fired ceramic
greenware (which is what they really are like), i.e. he’s keeping
them separated and stable so they don’t get whacked or bumped by
anything. If he’s chucking them in a bag and throwing them on the
floor of the car that’s definitely enough to cause the spalling.
Investment doesn’t like to be roughly handled, either manually or by
temperature changes.
Does he use an oven controller? If not, he’s most likely setting his
kiln at 7 1/2 or something so it rises and stabilizes at 1350 or so
after 6 or 8 hours. I know a lot of people that do that and seem to
have no problems. I on the other hand have never been able to pull
that off and get the level of quality in the castings that I want
with any degree of consistency. But maybe I’m just uber-picky about
my castings, or maybe my kiln isn’t up to doing that.
I think what happens when I try to “set and forget” is that the rate
of climb from room temp to around 800 or so is just too quick, so
there is no time for the water in the investment to dry out and for
the wax to melt and fully drain out of the flask (hence the need to
pause at 350) and then burn away (the pause at 700) before being
completely vaporized at the top temp. In addition to the investment
breaking down as a result of temperature differential and the water
boiling and expanding within the investment instead of being allowed
to gently evaporate, the wax starts burning and vaporizing before
it’s fully evacuated. This can cause further damage to the inside of
the cavity as the wax expands and begins to boil right next to and
even within the weakened wall. There is nowhere for it to go and the
result of that trapped water and wax boiling and burning within the
investment is that the investment walls literally start to flake off
so the vapors can escape - spalling. Even 2 inch flasks can’t keep up
with that rapid of a temperature rise without having at least some
degree of differential that can be potentially damaging.
A kiln can be manually controlled to achieve a nearly perfect
burn-out but it needs a bit of experimentation and babysitting to get
it right. In addition, unless the number and size of flasks is never
varied, the settings will need to be different for every load. Better
keep a pad nearby for notes.
It’s also a good idea to make sure the gauge and/or controller are
indicating correctly. You can find temperature cones or pellets for
ceramic kilns in a lot of different temperatures. They melt or slump
over at an exactly defined temperature, so you can make sure that an
indicated 1300 really means 1300 degrees in the center of the kiln.
Get a 1250, a 1300 and a 1350. The 1250 should end up as nearly a
puddle, the 1300 should be slumped over, and the 1350 should still be
standing tall when the gauge shows 1300 and the kiln has stabilized
for a while, or after a full burn-out with the controller set to a
max temp of 1300.
The buttons having a lacy edge in my humble opinion is an indication
that the metal is WAY too hot. When I vacuum cast, I look for the
edges and top of the button to be more or less round, sort of like a
deflated beach ball with a funnel at one end and no sharp edges
anywhere. When slinging metal, I look for a flattened version of the
same thing - still no sharp edges anywhere. A little catch on the
sides of the button usually means I’m flirting with disaster,
temperature-wise. When I can feel a sharp or rough ring around the
edges of the button while I’m quenching it, that tells me it’s time
to start swearing. I know I’m going to have porosity before I even
see the darn thing. If I get the lacy edges, I don’t even bother to
cut the castings off. I just start gating up more wax.
The metal temp needs to be just high enough to allow the metal to
flow into all of the cavity and no higher. The temperature of the
melt should always be the same regardless of what is being cast,
whether it’s a single 1/4 dwt prong setting or three 15 dwt gent’s
rings. The flask temperature is varied to lengthen or shorten the
time to solidification, lower temp (shorter flow time) for a heavy
piece or tree which fills easily and quickly, higher temp (longer
flow time) for thin and intricate pieces that will take a second or
two to fill. This is even more important with white gold. That’s why
we use a higher flask temp with white gold, to allow for the lowest
metal temp possible and still allow time for full flow before
solidifying.
Ideally, the goal is for the metal to stop flowing the instant it
gets to the farthest point of the cavity. If you’re not getting an
occasional non-fill, you’re probably using too high of a metal
temperature. If you’re getting too many non-fills, try raising the
flask temp before raising the metal temp. It’s sort of like trying to
get solder to flow. If the piece is hot enough and the solder’s still
not flowing, there’s something else going on and puttin’ the coals to
it ain’t gonna fix it. It’ll probably only make things worse.
White gold also needs to sit a while after casting. Quenching too
soon (with any metal) can cause it’s own set of problems, usually
cracking, brittleness and sometimes even porosity from uneven
shrinkage. I let all my flasks sit until I can handle them with bare
hands before I quench them. One more variable off the table, IMHO.
Too-hot metal can cause spalling, but again, it’s usually just one
more contributing factor. Icing on the cake, so to speak.
Yeah, poor castings make me crazy too. You can usually make them
work, but it’s just such an unnecessary time-waster. It takes almost
no more time to do it right and can save hours on the other end of
the process.
Keep after it Noel!
Dave Phelps
Noel,
If you like you can talk to the head caster at Stuller. Just a
thought… Email me off line with the number and I will be happy to
have Dennis give youa call… We call him Dr. Buzz
Andy “The Tool Guy” Kroungold
Hi Noel,
I must agree with Dave here.
As a casting company specializing in charms I have to cast a large
numbers of pots. I have found that on the rare occasions I have had
spalling it is usually caused by two things;
Firing the pots too fast or too hot. The investment tends to get
small hairline cracks that fill with metal when cast.
Rough treatment of the 'green 'pot. Once the investment in in the
pots they should be treated very carefully. I try to move my pots as
little as possible before firing.
I am amazed at the ‘she’ll be right’ attitude of some people. I have
been giving waxes from jewellers to cast that are just dreadful. Bad
waxes bad casting. I always try to make my waxes as perfect as I
can before casting. It is a lot easier to make a good wax than it is
to clean or fix a bad casting.
Cheers
June
Thanks for the explanation Dave, I will look closely at the
investment transition the next time I cast to try and identify the
phases you described.
Casting seems pretty easy until it stops working properly. The
troubleshooting sounds like it can be a nightmare, so many
variables.
James