I have an opportunity to handle metal artifacts from a local museum
in order to create replicas or jewelry pieces inspired by those
artifacts. Some of the artifacts are coins, some small metal
hardware, and at least one ring. I also have access to artifacts in
a collector’s home to use for this project. Since I have to make the
molds on site, I would like some suggestions of appropriate
materials to use. I have the two part cold molding silicone putty but
know there are other options. I will send my molds off to be cast.
I’m also thinking of using some pieces like a seal and stamping into
a blob of molding compound to yield a piece resembling a stamped
piece of sealing wax.
So, any suggestions of materials that have worked well for you?
I have an opportunity to handle metal artifacts from a local
museum in order to create replicas or jewelry pieces inspired by
those artifacts. Some of the artifacts are coins, some small metal
hardware, and at least one ring. I also have access to artifacts
in a collector's home to use for this project. Since I have to make
the molds on site, I would like some suggestions of appropriate
materials to use.
If accuracy is required it is not a trivial task that you are facing
with. I have some experience in restoration, so the process as
follows:
determine separation line. an object will have at least one or more.
do not rely on flexibility of mold material because when wax is
pulled, things getting distorted. It is fine for production
jewellery, not for museum copies.
Draw separation line and embed object in plasticine leaving exposed
only areas above separation line.
Cover object with even layer of plasticine, and cast a plaster mold
from assembly. Make provisions for keying the mold to other mold that
you will have to make. Lift the mold and remove layer of plasticine
covering the object. Put plaster mold back in place and pour rubber
compound in the space between plaster shell and the object. When set
put it aside.
Repeat the whole process for another part of the object bellow
separation line. if there is more than separation line, you will have
to do it for each and every segment.
When finished, assemble parts into the mold and take wax impression.
It will be exact copy except for wax shrinkage with is less than 1
percent. You can minimize shrinkage even more by painting was on the
inside of the molds with the brush. After 3 or 4 layers, assemble the
mold, pour some wax inside and keep rotating the mold until wax sets.
Since dimensions will be defined by first painted layer, the
shrinkage will be practically zero.
There will be casting shrinkage of course, but that can be
compensated by correct sprue design.
in the UK museums dont take kindly to the use of silicone
rubbers-dont know why but there you go so one must make moulds from
either latex or agar. Latex moulds are normally reinforced with all
sorts of mterials and then finally encased in plaster of paris. you
would then carefully make a pattern and then a working mould from
this pattern. Agar is a seaweed derived moulding material that is
used a lot for taking moulds of people’s faces for example and they
must be filled quickly as agar can decompose quite rapidly. Latex is
probably the best for small artifacts as it has some strength and is
easier to work with in the long term. You get good reproduction and
little chance of damage to the original as it is so flexible (hence
the backing material)
in the UK museums dont take kindly to the use of silicone
rubbers-dont know why but there you go so one must make moulds
from either latex or agar. Latex moulds are normally reinforced
with all sorts of mterials and then finally encased in plaster of
paris. you would then carefully make a pattern and then a working
mould from this pattern.
I wonder why that is? Agar is being replaced in dental and special
effects with the safe silicone rubbers, mainly due to its short
lifespan. When I used it years ago, if I wanted to keep the mould
from shrinking straight away I’d have to leave it in a bowl of water.
The best would be to take a scan of the object… if you could
afford to do it.
Casting latex has ammonia in it, doesn’t it? We exposed a copper
pattern with some ammonia the other day, wouldn’t this be an issue
with bronze artifacts?
If you are allowed to use latex that’s okay, but you have to be very
careful with making a mother mould out of plaster or fibreglass,
especially with fragile artifacts.
To me, the UK museums’ strictures against the use of silicone
rubbers on the objects in their collection sounds like a reflexive
preference for the old over the new. Every mold-making process
entails some risk to the models, but silicone rubber mold-making
compounds are fairly benign; at least they have a natural tendency to
release from things - unless they fail to set, that is. But even
alginate and latex can damage valuable specimens. Alginate is
saturated with water, which can soak into porous materials. Latex
emulsion is prepared with an ammonia base, which can react
unfavorably with various metals and finishes.
If what you want is a way to capture the 3d surface from
objects in museum collections without the risk of harm, you should
look into non-contact 3d scanning, which uses lasers to record an
accurate virtual mesh model that represents your object in three
Cartesian dimensions. Some take the form of cabinets with turntables
on which you place your original; a laser rangefinder sweeps it as it
revolves. It builds up an mesh by connecting the points it captures
with rows of tiny triangular facets. Other systems sweep the form
with laser lines that are captured by a pair of strategically-spaced
video cameras which enable the computer to extrapolate the XYZ
location of the surface at any given point.
If you’re trying to re-purpose these objects and utilize their
decorative qualities in new media, 3d scans give you a lot more
flexibility than molds. Once you have one of these scans in your
computer, it’s available for manipulation in various ways. Once
you’ve imported them into a CAD (Computer Aided Design) program, you
can freely scale the virtual model up and down, flip a left-facing
part to make a right-facing one, repeat it in a geometric array - the
sky’s the limit. Once you’ve created a virtual model in your CAD
program, you can send it to a service bureau with a 3d printer that
can give you a physical copy in a range of materials from plastic to
metal or glass.