OT/General Question about master sculpts and junk molds.

A sculpt is the original clay figure that you have modeled over an armature, whatever.
The sculpt may be modeled in Apoxie Sculpt, Polymer Clay (Sculpey, Fimo, Cernit...),
Air-Dry Clay (LaDoll, Premier, DAS...), etc.
Some clays are soft, do not dry out, and do not harden; so they require a waste mold.
A harder material is cast in the waste mold.

An example of this is an oil-clay (Plastiline) figure modeled over a wire armature;
waste molded in plaster or silicone rubber; then carving wax is cast into the waste mold.
The cast carving wax doll parts are then refined to use as patterns for the final molds.

An example of this is from Tim Bruckner's book, Pop Sculpture, where he models the
original figure (sculpt) in oil-clay; makes silicone rubber waste molds over the oil-clay figure;
then removes the oil-clay from the waste molds, and casts carving wax in them.
The carving wax, which is more durable than the oil clay, is refined and finished
to use as patterns for making the final silicone rubber molds.
He then casts resin in the final silicone rubber molds.

Tim uses old, chopped-up silicone rubber molds, to make the waste molds.
The chopped pieces are put around the oil-clay clay figure, and new silicone rubber is poured over everything.
Then, he puts the mold box in a pressure pot, to ensure that the new rubber is forced into
all the spaces between the old, chopped-up silicone rubber.
This way, his waste molds do not cost as much as making waste molds from new rubber each time.
He uses only new, fresh silicone rubber to make the final molds, for casting resin.

In her book, Learning to be a Doll Artist, Martha Armstrong-Hand models her original figure in oil-clay.
Then, she makes waste molds of the oil-clay figure using plaster.
She casts carving wax into the water-saturated plaster waste molds.
After refining the carving wax casts, she uses them to make the final plaster slip-casting molds.
When the final plaster molds are dry, she casts porcelain slip into them to make her final dolls.

There are numerous ways to finish the original sculpt for final molding.
Doll makers, sand them smooth, apply sealers, primers, and so forth, to prepare them for molding.
Depending on the modeling material that you have chosen,
the original sculpt may be used as patterns to make the final molds.
For example, from what I have read here, twigling models the original sculpt in Apoxie Sculpt,
then finishes the original Apoxie Sculpt figure for the final silicone rubber molds.
After removing the original sculpt from the final molds, it is general practice to make a
junk cast in the molds.
The junk cast picks up all the stray bits and pieces in the new mold, leaving it clean for subsequent castings.

It is my feeling, from reading your post, that you are somewhat unclear
about the difference between a waste mold and a junk cast ???
Hopefully, you now have a better idea what the differences are?

Original sculpt --> waste molds --> cast intermediate doll parts
Refined intermediate doll parts --> final molds --> junk cast --> final castings

--or--

Original sculpt --> final molds --> junk cast --> final castings.

It just depends on what you want to do, and how you are doing it.

Have Fun !!!

 

If your original set of molds is good and gives you the results you want, I don't see any reason to make another set. But as KW says above, you'd probably want to make a test cast.

 

The key is what material the original sculpt is made of.
If the original sculpt is hard enough to be finished smooth, and is tough enough to test string,
then you can make the final molds directly from the original sculpt.

If the original sculpt is too soft to be test strung, and cannot be finished smooth, then it will need
to be waste molded so a more durable material can be cast, which can be test strung and smoothed.

So if your original sculpt is made from Polymer Clay or Epoxy Clay, for example, they are both hard
enough to be finished smooth, and they can be test strung, so they do not need to be waste molded
to cast an intermediate material because the original material already has the desirable properties
for making final molds.

A waste mold is used to translate a soft modeling material into a harder material for refining to make final molds from.
The waste mold is not needed if you do not need to have a soft material translated into a more durable material.

No matter what, you will want to make a junk cast in your final mold before running your production.
The junk cast picks up debris from the new mold, and that is why it is called a junk cast.
Junk casts can be used to practice faceups, can be used to do modifications, and all sorts of things.
The junk cast does not have to be thrown away. It can be useful, especially if you are learning.

Have Fun !!!

 

I have never heard of the term junk mold.

Actually, the term waste mold, in traditional sculpture, refers to a plaster mold that is hand-flicked over an original clay sculpture. Thin shims are placed in the clay sculpture before a color coat is applied, in order to create a parting line. The first coat of flicked plaster is a color coat. The color coat is generally thin, and is flicked on the sculpture, from bottom to top, with a back-handed motion, which forces the plaster into all the details. When the front of the clay sculpture is covered, the sculpture is turned and the back is covered. The color coat is then covered, front and back, with a thick coat of white plaster. Once the thick coat of plaster has set, the mold is split, the shims removed, and the original clay is dug out of the mold. The waste mold is then cleaned thoroughly of all bits of clay, and a parting agent is applied inside the mold. The waste mold is put back together again, tied up, and positioned to pour a plaster casting. Once the plaster cast has been poured, and is thoroughly set up, the waste mold is chipped off the cast plaster with a hammer and chisel. The color coat tells the sculptor that she is getting close to the cast plaster, so she can chip off the waste mold more gently. The cast plaster is referred to as the original plaster. The original plaster is then refined and worked on until it is deemed ready to make the final molds. The final molds used to be made from gelatin, but are more frequently made from a polysulphide rubber, such as Black Tuffy in modern times. In this case, the first mold is called a waste mold because it is destroyed when it is chipped off the original plaster. The waste mold, in this case, is used to translate a soft material (oil-clay), into a material that is more durable, and can be handled for making the final flexible mold.

In the book Pop Sculpture, Tim Bruckner describes making waste molds from old, chopped-up silicone rubber molds, combined with a small amount of fresh, new silicone rubber, to hold the chopped pieces together. He makes the silicone rubber waste mold over the original oil-clay figure. Then, he opens the waste mold, removes the original clay, cleans the mold, and casts carving wax into the waste mold. The carving wax is tough enough to be refined for making the parts for the final sculpture, which is then cast in silicone rubber molds that are all new rubber. Once again, the waste molds are used to translate a soft material into a harder material that can be refined and finished in order to make the finished figure. He calls those first silicone rubber molds, waste molds because he chops them up later on, to make other waste molds for other figures. Actually, his first waste molds could probably be kept for awhile, because silicone rubber has a good library life. However, I would imagine that he probably chops up all his old silicone rubber molds to use in waste molds. So there again, the waste mold is destroyed.

In Learning To Be a Doll Artist by Martha Armstrong-Hand, Martha makes multi-piece plaster rough shell molds over her original oil-clay figure, which was modeled over a wire armature, supported by an armature stand, on a modeling board. She models the figure, removes it from the armature support, cuts the figure apart, then makes the multi-piece plaster rough shell molds over the oil-clay parts of the figure. She uses the plaster rough shell molds to cast carving wax doll parts, which she refines and finishes for making the final plaster slip casting molds. She pours porcelain into the final molds to make her porcelain BJDs. The plaster rough shell molds are not destroyed when she removes the carving wax castings. However, the plaster rough shell molds are made using a dry-lake method of mixing plaster, which is not as consistent as making plaster molds for the final slip casting step. For the final molds, the water and plaster are measured so that an accurate ratio is the same for each mold. This way, the final mold sucks moisture from the slip consistently, so the mold does not produce a thin wall on one side and a thick wall on the other (which you can get if the pieces of the mold are not the same consistency). Here again, the first molds are used to translate a soft material into a more durable material for making the parts for the final sculpture. Then the final molds are made over those refined doll parts. You could actually keep the plaster rough shell molds, but I think they would quickly use up valuable studio space, so they are probably tossed in the dust bin after the carving wax parts are made; so they are also waste molds of a sort.

I use hot-pour moulage as a waste mold material for translating sculpture wax, or oil-clay original into carving wax. The hot-pour moulage mold cannot be stored for very long, so these molds must be used to cast carving wax right after making them. They can, however, be chopped-up and reused. I must put the chopped-up pieces in a sealed jar to store them. The hot-pour moulage is heated to melt it for making the molds. Because they have a lot of water in them, they are perfect for casting wax or plaster into. Water and wax do not mix. I use the hot-pour moulage molds in the same way that Martha uses plaster rough shell molds, that Tim Bruckner uses silicone rubber waste molds, and that traditional sculptors use plaster waste molds, ie. to translate the soft oil-clay into a more durable material for further work, in order to make parts for the final molds. I like the hot-pour moulage over plaster because the moulage can be reused. I place a very high value on sustainable, reusable materials. They are also very economical, and also good for the ecology as well. Moulage is made from seaweed, so it is a renewable resource.

Have Fun !!!

 

I was wondering where you picked up that term.
Learning To Be A Doll Artist by Martha Armstrong-Hand has a chapter on making doll wigs.
See this link for an excerpt from her book about ventilating doll wigs.

 

I use LaDoll clay to sculpt my dolls and when I did my own molding, I wanted to skip the junk mold stage and go straight for the 'real deal'. In my case, it didn't work. Because I wasn't able to properly test the joints, due to the softness of the clay, when I made my first doll cast, there were so many things that needed additional work, that I needed another molding round.
Another thing that happened to me was that the primer layer started to crack during molding, leaving imprints in the mold. I had to redo most of the biggest molds.

So, while it is possible to skip the junk molding, there are so many things that could go wrong during the process that you will have to expect additional costs. Some molds won't come out the way you want them to, sometimes the silicone won't cure properly for whatever reason and sometimes you'll see an error in your master that you'll need to fix.

Casting is expensive, not because of the resin, but because of the silicone. This is exactly why I decided to let a casting company do the hard work: it turned out to be cheaper than making my own casts and the final results will be better.

 

I also sculpt using airdry clay, then prime it. And I don't think you can expect to get perfect casts out of your first set of molds. I think you can make a perfect mold...but may find issues with the sculpt itself that you didn't/couldn't see on the original despite all the sanding/priming/etc. My method is to use a low cost silicone for the first set of molds on a new doll, but to expect to make a second set of molds for the problems I hadn't found yet and budget for that. Using a casting company is cheaper if you don't like to do moldmaking and casting, but you may end up making a couple of sets of molds even if you send your doll out to the casting company due to sending a resin master that you've primed up for casting (unless you just send your original, which I wouldn't do personally) -- it's all dependent on how perfect your original is. :/ It's a research and development process and you have to figure out what works for you. Good luck!