After making an RTV mold of a necklace segment I found that the cast
product had small defects. First there was some indention along the
separation line of the mold, and secondly there were a few pinpoint
holes.
At first I thought the pinpoint holes were the result of porosity,
but careful examination showed that the holes were already in the
wax copies. My initial method of repairing this was to grind down
the problem areas in the cast pieces, a most tedious job.
My question: is there a sealing compound, say something like the
whiteout used for covering typing errors, that is appropriate to fill
the small problem spots in the wax copies?
Stan, check out Disclosing Wax at Gesswein product # 261-6360 it
is designed to be applied with fingertips and smooth over defects
and then burnish back to fill voids and detect high spots. You can
also heat glaze the surface of the waxes to make voids appear and
also to fill them, but this takes a practiced touch. It is the
technique I use and I use a hot air torch designed for the
electronic industry that runs off butane. Frank Goss
Repairing pinholes and such in molded waxes is actually even easier
than what you ask. Just go into the mold itself, and porosity is
raised bumps. Just snip them off, or burn them, depending on which
rubber - silicone doesn’t melt, for instance, and POOF!- no
more porosity.
My question: is there a sealing compound, say something like
the whiteout used for covering typing errors, that is appropriate
to fill the small problem spots in the wax copies?
Hi Stan; Yes, there is. It’s called “disclosing wax” (21-0256) and
it’s used in the dental tech industry, but I’ve ordered it from
Stuller. Stuller also has what they call “repair waxes” (21-0360 &
21-0361) in their tool catalog. I’m using the disclosing wax. It’s
white and creamy in texture, so you just smear it on. I’d like to
try the repair waxes though, so next time I order I’ll try them. The
disclosing wax is very soft, perhaps the repair waxes are a little
firmer, which would be nice. Another thing I use the disclosing wax
for extensively is in stone setting. If I’m setting in a bezel or
channel, I smear a little over the stone, wave a torch lightly at it
and it flows down around the stone, keeping it from rattling in the
setting as I’m hammering bezels and channels down. It also squeezes
out around the stone as the metal closes, which allows me to guage
how close I am to the stone. It’s very easy to steam it out and
finish the job, or put it in a little jar of naptha in the ultrasonic
cleaner.
My question: is there a sealing compound, say something like the
whiteout used for covering typing errors, that is appropriate to
fill the small problem spots in the wax copies?
You can get a little jar of a white paste wax called disclosing wax.
It’s a dental wax. A little on a fingertip will smear over your
model filling minor holes and depressions. But it’s not perfect,
your casting will still be slightly rougher there.
Personally, I just use a wax pen, with a pointy tip, and just a
little bit of the same injection wax the model is made of, and touch
to hole or defect. The tiny bit of wax on the pen fills it to a slight
bump. You can scrape that off with a scalpel or other wax tool if
you like, especially while it’s still warm, or just leave it and take
it off in the casting when you polish the casting. Low spots or holes
in a casting often require a LOT of material to be taken off,
sometimes with considerable damage to the design. But a slight bump
comes off in a seconds during just normal lapping/polishing
operations, with no damage at all to most non-textured surfaces.
Hi Stan. Sounds like the best and easiest solution would be to
correct or remake the rubber mold. Sometimes I will use my wax pen
and “burn” off imperfections in the rubber. The indentations along
the parting lines sounds like too much pressure from the injector.
RTV rubber is so much softer than the vulcanized type so you have to
be really careful on the pressures when injecting. There is also a
wax called disclosing wax that can be smeared on the wax pattern with
a finger or q-tip to fill small imperfections. Best wishes, Ken Sanders
Ferris makes two waxes, a green and a red one, the last being extra
soft, but not as soft as disclosing wax (it is not creamy, but more
like lipstick (I guess)). They come in little jars and work well. You
don’t need a tool for it, just rub it in with your finger. But I
think that (blue) wire wax works well too when warmed a bit. Best, Will
I have been reading with deep interest, the exchange relative to
repairing tiny voids in wax patterns. There is clearly a number of
products being sold which help repair the defects, as well as plenty
of astute methods of repair.
Solutions such as snipping and burning defects or bumps out of the
mold cause me to ask–why are there bumps in the mold? There seems
to be a good deal of this going around, given the number of people
who have ready solutions to the problem.
Your mold rubber should provide you with a perfect copy of your
model. If there are defects in the model, correct them. If you end
up with defects in the mold pattern just the same, then your rubber
is either defective, or your mold making technique needs help.
I appreciate all of the very astute help offered, but there is one
misconception I wish to correct. That is that silicone RTV is
"softer" than the vulcanizing rubbers. Actually, some are and some
are not. You can buy silicone RTV in hardness ranging from 25 Shor A
to 90 Shor A durometer. The natural rubbers are in the range of 35
to 40, while the heat cured silicones range up to 70 Shor A.
I have been developing and manufacturing mold rubbers and injection
waxes since 1990. I have developed natural rubbers, heat cured
silicones and liquid and putty RTV types.
I welcome any opportunity to help you clear up some of the mysteries
of the process or any problems you may have with the materials you
currently use.
Bill Mull
Zero-D Products, Inc.
800-382-3271
440-942-1150
Thanks to all the replies to my SOS on how to repair pinpoint holes
in my injection waxes. I tried both the ‘dab of injection wax’ and
the ‘disclosing wax’ methods with success. The one I found most
difficult to accept, namely ‘make a new RTV mold’, turned out to be
quite relevant. It is indeed remarkable to be able to draw on the
collective expertise of the orchid community, and for that privilege
I am truly grateful!