Reproduction Resin

I have model that I wish to reproduce. last night, a Buddy told me
that there are resins that shrink and will allow to make even smaller
models. What is the name of this Resin and where do I find it.

Achbar

Achbar ibn Ali wrote:
I have model that I wish to reproduce. last night, a Buddy told me
that there are resins that shrink and will allow to make even smaller
models. What is the name of this Resin and where do I find it.

Achbar

The best and cheapest is gelatine.
Make it hot, poor it into your silicone mold and put it in the fridge.
Percentage rate of shrinkeage you might determine by concentration of
gelatine. Drying of very weak forms is best by floating in pure alcohol.

--
Heinrich Butschal
casting technologies
http://butschal.de/werkstatt

On Fri, 14 Nov 2003 02:04:21 GMT, in rec.crafts.jewelry Achbar ibn Ali
wrote:

I have model that I wish to reproduce. last night, a Buddy told me
that there are resins that shrink and will allow to make even smaller
models. What is the name of this Resin and where do I find it.

Achbar

There is a class of dental impression materials called aginates. These come as
a dry powder which you mix with water to give a somewhat gelatinous putty like
material that can be used to make a mold or impression of almost anything. The
stuff sets up in about a minute, some of them faster, some slower. The
resulting mold is not durable, and as it dries, it shrinks. it's intended to
be used for making a wax or plaster casting from the impression fairly soon
after the mold is made, which would give virtually no shrinkage. But if you
wait, you can get reduced size impressions. It's been a while since I last used
the stuff (decades, actually) but as I recall, you can get shrinkage of up to
about 30 percent or a bit more, from a single mold, and of course, if you need
more, you make one impression at whatever shrinkage it gives you, then make a
new aginate mold of that impression, and let that one shrink, and repeat the
process. I recall one art student (this was back in the 70s) in one of my
sculpture classes, who'd thought it would be cool to make such an impression of
his erect penis. He turned this initial impression into a whole series of
progressively smaller and smaller wax models by making new molds of each
somewhat shrunk model, until the last in the series was about an inch, then
cast all the waxes (I think he'd made a series of about 8 of them, in bronze and
made a piece from this shrinking series. I don't recall the piece itself as
having been especially successful as art, but I remeber being impressed by the
retention of detail from one reduction to the next was very good.

Rio Grande, our well know jewelry tools supplier, I believe carries a version
of this type of material supposedly optimized for jewelry use, under the brand
name "reducit". It's probably best used for simpler flat items that can be made
with an open faced mold, rather than a mold needing cutting and fitting to
remove a wax, since as it dries, it gets quite stiff.

Hope that helps.

Peter Rowe

"Achbar ibn Ali" wrote in message
...
I have model that I wish to reproduce. last night, a Buddy told me
that there are resins that shrink and will allow to make even smaller
models. What is the name of this Resin and where do I find it.

Achbar

Reading the answers given to your question worry me quite a bit.
Surely the rate of shrinkage is going to be proportional to the surface
area/volume. A thinner area will shrink faster than a thick one. I can't see
how you'd make a perfect scaled down version of an original cast at all
acurately using gelatin or alginates. Sorry.

On Mon, 08 Dec 2003 18:34:13 -0800, in rec.crafts.jewelry "CheshireCat"
wrote:


"Achbar ibn Ali" wrote in message
. ..
I have model that I wish to reproduce. last night, a Buddy told me
that there are resins that shrink and will allow to make even smaller
models. What is the name of this Resin and where do I find it.

Achbar

Reading the answers given to your question worry me quite a bit.
Surely the rate of shrinkage is going to be proportional to the surface
area/volume. A thinner area will shrink faster than a thick one. I can't see
how you'd make a perfect scaled down version of an original cast at all
acurately using gelatin or alginates. Sorry.

Actually, the shrinkage, while not totally uniform, is pretty much linear. Both
the gelatine and Alginate products shrink through slow evaporation. You don't
allow the surface to shrink faster than the interior (which would crack the
surface), and after that, the shrinkage is a percentage of any linear dimension.
Some thin large flat areas *might* shrink slightly more in the center than at
the edges, giving you very slightly concave surfaces, but it's not at all as
much as one sees in, say, injected wax models that are shrinking as they cool in
the mold. The alginate reductions I've seen are surprisingly accuratly scaled.
At least within the limits of being visually accurate. I've never tried to
check one with micrometers to see if it's perfect, and to be honest, it's been
years since I used the stuff, but the few times I did this, shrinkage seemed to
be quite uniform overall.

Peter

Peter W. Rowe wrote:
On Mon, 08 Dec 2003 18:34:13 -0800, in rec.crafts.jewelry
"CheshireCat" wrote:


"Achbar ibn Ali" wrote in message
...
I have model that I wish to reproduce. last night, a Buddy
told me
that there are resins that shrink and will allow to make even
smaller models. What is the name of this Resin and where do I
find it.

Achbar

Reading the answers given to your question worry me quite a bit.
Surely the rate of shrinkage is going to be proportional to the
surface area/volume. A thinner area will shrink faster than a thick
one. I can't see how you'd make a perfect scaled down version of an
original cast at all acurately using gelatin or alginates. Sorry.

Actually, the shrinkage, while not totally uniform, is pretty much
linear. Both the gelatine and Alginate products shrink through slow
evaporation. You don't allow the surface to shrink faster than the
interior (which would crack the surface), and after that, the
shrinkage is a percentage of any linear dimension. Some thin large
flat areas *might* shrink slightly more in the center than at the
edges, giving you very slightly concave surfaces, but it's not at all
as much as one sees in, say, injected wax models that are shrinking
as they cool in the mold. The alginate reductions I've seen are
surprisingly accuratly scaled. At least within the limits of being
visually accurate. I've never tried to check one with micrometers to
see if it's perfect, and to be honest, it's been years since I used
the stuff, but the few times I did this, shrinkage seemed to be
quite uniform overall.

Peter

Full ACK, its really important to reduce in a slow process.

--
Heinrich Butschal
casting technologies
http://butschal.de/werkstatt