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Sculpting and Moldmaking Overview and Links

Written by Mike Brent

I thought I'd post up some of the tips I've collected from various online sources and personal experience on the subjects of sculpting and moldmaking, very useful skills for any fabricator to possess and constantly sharpen. First up a primer on some of the various tricks you can use with polymer clay. The finishing techniques will also work with plasticene:

MXING POLYMER CLAYS

Different polymers have different qualities. Premo is very flexible and comes in a great range of artists colors, so it adds flexibility (which equals strength) to the finished sculpt, and you can blend your own custom colors. I saw that the Shifletts were sculpting with these cool browns and reds, and I just had to try it. It actually makes the whole process more exciting. But... stay away from anything really bright or distracting. You want to stick with very neutral colors that remain in the 'middle' zone of the value scale. In other words, if you would take a picture of it and bleed the color away, it would be a middle grey rather than light or dark.

Remember that while you're sculpting, all you have to go by is what you can see, and that boils down to shadows against your material. If the material is too light the shadows are too stark, and if it's dark they're too close to the same value. The same applies to bright or distracting colors... avoid the temptation to sculpt in shocking neon pink! Lighting is important while you sculpt too... I often think about the kind of lighting I'll use in a film and try it on the sculpt in-progress, to see what the shadows are doing. I actually sculpted Ahab with a strong raking light from directly above, because that's the kind of lighting in the picture I used for reference, and I would squint at the sculpt and turn it slowly, lookng at the shapes made by the shadows. Now as a result, he has very strong planes in his face, and they catch the light nicely.

Fimo and Cernit are much denser than Super Sculpy or Premo, and they can firm up the clay body, so you don't accidentally squish out those details when you pick it up or hold it while sculpting. They also make the finished and baked piece much harder... like porcelain as opposed to plastic. But these denser polymers are hard to 'condition' (knead), which you must do before you can sculpt. Most people will use a pasta roller. Once I got mine, my life got a lot more pleasant! Now I have an air-tight ammo box from the army surplus store where I keep my pre-mixed custom blends, and often I'll put some of them together and run them through the pasta roller a few times to make new colors/blends. I mix Super Sculpey, Premo and Cernit for my ultimate blend. But again, the main component is always super sculpey... you don't need muchof the dense stuff, because it's hard to work with and gets crumbly. Just a dab will do ya. Use small pieces and try some different proportions to find your optimal mixture.

Polymer clays will respond to pretty much the same techniques as plasticenes. These include Texture Stamping, Sculpting Through Plastic Wrap and Brushing Down With Solvents as well as some more basic tricks.

Texture Stamping

You can easily impress textures into the clay by pressing textured objects against it, such as various kinds of cloth, the rinds of certain fruits and vegetables, or basically anything that's got the right kind of texture. And you can create your own texture stamps as well. Using either epoxy putty or a polymer clay, just make a sort of handle shape with two ends... one large and roundish and the other much smaller for tight detail work, and start texturing it. Tap the end of a nail against it.... press objects into it... add fingerprints if you want more subtle detail on top of the main texture... just go nuts with it! And of course you can do all this stuff to the clay itself too, not just to the texture stamp. Lately I'm moving toward very textured surfaces that won't be slick and shiny, and I like to use a lot of layered fingerprints to break up that slick surface. For more on texture stamping (and lots of other great tips) check Dan Perez. He also has a great section on making molds. And of course, Smellybugs Maquette Tutorial is probably the ultimate resource for learning how to sculpt with polymer clay.

Sculpting Through Plastic Wrap

This is for making shallow, round-edged wrinkles. It doesn't work for deeper wrinkles or cuts that need to have a sharp edge. It's very simple... just lay a piece of cling wrap over the area you're working on and sort of draw the ines through with a tool. Not anything too sharp... obviously you don't want to cut through the plastic. A ball-ended stylus is great, or the edge of my mini spoon tool works like magic. Different thicknesses of plastic will make a difference. I like the pretty thick stuff that CDs and DVDs come wrapped in.Brushing Down With Solvents

This is good for getting a very smooth surface... I always like to do it when I'm just about finished, though often I'll follow it with some texturing. Turpenoid is a very strong aggressive solvent, used in oil painting. It's odorless, which is nice. It will actually dissolve the micro-surface of the clay amd sort of let it flow over itself, and then redeposit the liquid clay... filling in little holes. But it's awfully strong for most purposes. I generally just use alcohol. 91% isopropyl is the most recommended variety. This doesn't attack the surface nearly as much as Turpenoid or other strong solvents like Bestine or Acetone (both very flammable and highly toxic... not recommended). Lighter fluid will work too - I believe it's also called Naptha sometimes.

But again, a dangerous and nasty chemical that you wouldn't like to play with. For gentler smoothing, some people like to just brush down with water or saliva. It can work for very minimal smoothing, but watch out because water can cause "moonies", which are small crescent-shaped cracks in the surface that appear when baking. Not pretty... though they don't seem to affect the actual surface... paint generally hides them completely. I've also found that a fairly stiff brush used without anything on it is good for getting a kind of gritty surface. Experiment on a scrap chunc of clay... it can be hours of fun and entertainment. Oh, and the kind of brush you use is important too. I like one that's not too soft, like a Mongoose or Badger hair brush. Usually a short flat or filbert. If you're using a strong solvent you might be able to get away with a soft brush like a sable, but be careful... the softer brushes tend to shed bristles, and since you're into the final detailing here you don't want to have to dig around to pull stuck bristles out of the clay!

I'll list any links to on-site threads dealing with related subjects here, starting with this one:

SCULPTING TUTORIALS & DEMOS:

ONLINE SUPPLIERS:

Suppliers in Australia - NSW :

Suppliers in Australia - Vic :

UK suppliers:

MOLDMAKING/CASTING TUTORIALS:

Not quite exactly what to do with all this, but it's too good not to post in here, so I finally decided to just pull all of it directly from the Sculpting Forum and deposit it here bodily. First, here's the Gore Group tutorials (image intensive, and no descriptive text) on their own site:

...and below are two detailed write-ups, the first by Martin Canale explaining some of what's going on in the pics, and the second by Ralph Cordero detailing what's happening in the moldmaking part of the tutorial. Sorry, these are pretty big, but I don't know how else to do this:

Equipment

Sculptors always have a wide selection of tools which he or she feels most comfortable using. In fact, we have lots of modelling and dental tools, but we use to work just with five or six of these whilst sculpting a figure. And don’t you ever forget you have some great tools stuck to the very end of your arms, most useful for the early stages.

Starting off

It’s a fact that preparation is the key to success. You have to make a good research and gather as much reference material as possible. One thing you should keep with you all the time is a book on anatomy, especially when planning the proportions of your figure. This is a crucial part of the process, so take your time, have fun, and do some investigation.

Perhaps you like the idea of having a proportionally correct photocopy of a figure and resize it depending on the scale of the piece you are going to work on. We strongly recommend to use these same resized figures for the armature planning.

Armature:

An armature is just a framework that provides the basic form and proportions for your figure. It also makes the sculpt much more resistant and lets you to pose it in whatever position you require. We use two sizes of wire to make an armature: for the main part we use aluminium paper (to give volume to the thorax), after that we cover it all with fast action epoxy clay.

You can find many kinds of wire in your local shops but it all comes down to budget and preferences in the end.

We use to work the character’s head and hands separately. Why? Well... these two areas need much more detailed work than the rest. Needless to say, making them individually helps to get to those hard to reach places. First of all we sculpt the head, since it is the focal point of every figure, the most important part of the kit. What does this mean? It means that nothing else matters if the head isn’t right.

For the head we use a piece of wire. We make something similar to a circle in one end, where it will be made the head. Then we cover it with epoxy clay until it gets half its intended size. This way we make a base where we should sculpt all the rest. Once the head has been sculpted, it can be attached to the main armature by cutting the brass tube to the

correct length and slotting it over the neck. This way you can also pose the head and remove it if any correction is needed.

The Main Figure:

Once the head is finally complete and in place you can start building up the clay on the main body of the figure.

You should over exaggerate the pose, since the addition of clay reduces the impact of what it was supposed to be a dynamically posed figure.

Many artist use to bake the sculpt after applying a layer of clay over the armature, but not us. Sometimes further corrections are needed. And we always build up the form as a whole, not in one section at a time cause this way you have more chances of loosing body symmetry, size and/ or proportion.
Again, try to get as much reference material as possible. When you are making the muscles, have in mind that certain muscles take different appearances depending on their orientation and action.

Don’t rush to make further details on the muscles unless you are completely sure they are well placed in the figure. The final result will surely be worth the patience.

If you are happy with the basic muscle structure, you can start refining the figure…….

…….and also to start working on the figure’s clothes, that’s why we recommend you to have some reference material about these matters too (a good collection of books may be needed). When we say "refining" we mean the process of smoothing and removing all possible imperfections on the clay. Right after that comes the finishing details addition.

Now, if you want to make copies of your new figure -castings-, there are some considerations you should attend to. Some sculptors make all the figure as a whole and then cut it using a little saw (although this might produce poorly fitting pieces in the final product sometimes). That’s why here, at Gore Group’s headquarters, we use to test-fitting the pieces continually, so as to ensure a perfect fit in all our figures.

This part of the process needs to be explained in detail so as to achieve a good fitting of the figure’s pieces. Talking about a head or an arm (usually these are the pieces to be separated) we had already prepared the wire snap-on. The "female" piece in the base, the "male" piece in the head, arm or whatever.

That’s where we tie the string (try to get from an supplies shop what we use to call invisible string, used for shortening trousers and such. This invisible string has the width of a hair and is almost as resistant as the strings used for fishing) leaving the two ends hanging from the piece, being convenient to unite both ends with a tiny piece of scotch for working freely.

Now we can start working on the figure as if it were a whole, with the advantage once we finish the piece to be separated we have the string (previously inserted trough the wire) for cutting through the fresh sculpey. All we have to do now is to get the string from both ends and cross them until the piece has been completely cut off.

Done this, our figure is ready for the oven. Voila!"

********************************************************************

...And here's Ralph Cordero on the moldmaking process, shown in the last group of pics:

"Hey Gang, just wanted to rundown what is going on in the wonderful tutorial pics that Martin has been so kind to share with the board."

"Martin starts off by figuring out the best way to "hang" the sculpture in the mold box, keeping in mind not to position the sculpt to close to the mold walls. You also have to keep in mind resin flow {for when you are casting resin} if you find possible air traps you will need to add or cut air vents later."

"Once you have figured out your box configuration, you build your box out of pressboard or formica covered boards {you can get shelf stock boards at your lumber store}."

"Next you drill your holes for your screws. Use a countersink to make the screw heads lay flush to the board."

"The reason to use a smooth surface for the mold box allows for a clean surface on the mold exterior. This makes it alot easier to put your box back onto your mold when you are casting. Woodgrain form plywood may not register back exactly."

"Once you have figured your sculpt suspension{usually worked into being your pour sprue} you grease your boards with petrolium jelly, or crisco, or other greasy medium, this keeps the silicone from sticking to the pressboard, probably not needed for formica, but sometimes silicone can bond to the most unexpected surfaces."

"Now you are ready for silicone, there is a formula to measuring the material, I believe the method was height x width x Depth and then you multply that by the weight of a square inch cube of silicone. I will varify that and get back to the board, I just eyeball the stuff."

"Now for the no bubble part. There are two meathods to this. Evacuating your silicone with a vacuum pump, or pressure casting the entire mold assembly in a pressure pot."

"First you need a good pump that pulls an absolute vacuum of 29 {outer space is 30} anything less wont cut it, I have tried."

"Robinair SPX cooltech 6CFM high performance vacuum pump is great and is available for around 260.oo or less over at EBAY."

"You can get a vacuum chamber for around 50.00 over at Ace glass company. It is a plastic chamber ready to rock out of the box."

"You can pull 2000 grams in the chamber. Or you can make one out of a heavy duty stock pot and a 1 inch thick lucite top. You will need to add some kind of rubber gasket to create a solid seal. Add some proper fixtures and you can do larger than 2000 grams in this config."

"You let the silicone rise and fall, debubble for a few more minutes and you are ready to pour. Pour your silicone slowly and from a very high position to create a thin strem, this will prevent any large bubbles from being placed into your mold thru pouring."

"Now many studios skip this step and place the entire mold setup into a large pressure pot and pour the silicone into the box and pressure the entire setup to a pressure of about 40 lbs. This does the same thing that pressure casting of resin does. Basically no bubbles. And the silicone is pushed into every nook and cranny. If you are casting a piece with mega mega detail this is an excellent way to go even if you are evacuating your silicone. You can also do fast cast silicone{ultrafast catalyst added}."

"Typically you cannot deaire silicone with fast cast additive, the bubbles get trapped in the evacuation process basically your silicone will swell and stay that way, very reminicent to exspensive rubber froth. So you place your set up in the pot and pour, close and wait. You can produce bubble free quickie molds in an hour."

"There are two drawbacks to this method #1: if you have Caught an air pocket in your sculpt it can implode under the pressure, so you will have a mold of a wonerfully craced apart sculpt, not fun."

"#2 : You must always use a pressure pot that can handle the pressure for 24 hours. If not the bubbles will reform as the pressure neutralizes to regular air pressure. The mold rubber will swell and distort your mold horribly. Best bet is to always keep some extra silicone from you batch in a small cup and lable the time on it and place the cup on the pressure pot. Check it for hardness and demold your molds once the sample has kicked."

"Now comes the fun part, surgery:"

"This usually starts at the mold sprue. Most moldmakers will mark the mold line they want to follow with a sharpey marker."

"This makes it very easy to keep your parting line just where you need it, thus giving you a great seam."

"We use medical spreaders, they look like scissors with curved forks on the ends and a locking mechanism at the base handle. They click into increments as you spred the mold rubber."

"You start with an initial cut, we prefer #12 sheffield steel #12 curved blades as well as # 11 blades both in a milton #5 scalpel handle."

"You make your cuts in a zig zag pattern, gently wiggle your blade left and right as the blade glides thru the rubber, the depth of the cut depends on the size of your mold. The zig zags act as tiny resistration points and will keep your mold alignment just right. This takes ALOT of practice, so do so on some scraps not on an official piece. You must be very careful not to cut yourself, these are surgical blades and can cut deep."

"Once you have made your initial cut you insert your spreaders and begin spreading your mold and cutting. Spread and cutuntil you hit your sculpt. I like to lubricate the blade after every few layer cuts with vasoline or olive oil, makes the blade glide thru the rubber with great ease. Follow your marker line until you are done."

"Now for casting, if you have planned your mold right this is as easy as mix the resin amount and pour, place in pressure pot and close, bring pressure anywhere from 40 to 80 psi <depends on what you are casting,things with thin delicate detail benifit from higher pressure."

"...And, wait. Pressure casting is the only way to go, far fewer reject factor."

"If you find you are catching bubbles then you will have to cut vents into your mold. This can be done with a brass rod the size of the hole you are needing to cut to make the vent function. You countersink the interior of the rod until it leaves a close to razor sharp edge. This can be done with a #11 xacto blade run along the interior brass edge surface until it is sharp."

"Now you grease the tube interior and plunge it thru the rubber wher you need a vent. A tube pushed thru silicone will leave a smaller hole than that of the tube diameter so plan on going a little larger to get the right size hole. You can also run the tube thru the mold surface to create a half gouged out hole on the surface as well."

"Gang boards are very important for your larger molds, they will support your rubber and keep its original form, and will keep your mold from being tweaked out from rubber bands and mold straps."

"As for mold duration it depends on a few factors. The petroleum content of your resin,{resin contains petroleum products that can breakdown mold rubber, if your resin reaks ala BJBs TC 810 it has more oil in it}
You need to use a good quality rubber as well, we use Silicone INC's GI 1000, rubber. It takes 18 to 24 hours at 70 degrees to cure, and will last approx 2 years on a shelf before decay begins, basically on a mold that age you will lose little bits of rubber in your castings until your mold rubber begins to split and then its into the garbage heap. DO NOT use this rubber as cut up filler, it will delaminate from your fresh poured rubber and you will have a mess of a mold."

"Martin mentions cutting up discarder molds, this is a great way to conserve and recycle what is the most expensive part of our hobby/ job."

"You can also cut up the leftover rubber from the bottom of your buckets."

"Just make sure all the rubber has been catalyized and is not tacky."

"Wash your recycle rubber down with a little alchohol and you will be guaranteed good adhesion."

"Best recommendation I can make is to practice on a gi joe size head at first. Mold it in a paper cup {hot cups are plastic lined} And cut it up the back. Then try another one and cut it up the sides. We mark our sculpts with a sharpie marker, anything that will mark your model will due, like a soft lead pencil. You can then take pins and poke them thru the cup and have them almost touch the model. Lock these in with a little hot glue."

"These will give you a trail of micro holes that you can follow on the exterior of the mold as you cut. You start at the neck, cutting to the mold exterior. Repeat this with the zig zag cuts."

"Xacto #11 blades will work fine but are not as sharp as the scapel blades. So you may go thru a few."

"As for the clay wall approach, we use it as well, all depends on sculpt shape and mold size. If the part we are molding has archaic lines that would make a mess of a mold to cut open we will do a two piece mold or a matrix mold {mold with jacket} also depends on project schedule and budget. A cut open mold is the fastest mold you can make."

"The seams on a properly cut open mold are practically non existant, the reason for this is the lack of any debris , such as minute left over water clay from your mold process. A good mold maker will make you a beautiful seam, but your mold will cost you more."

"It really is a matter of choice, I used to clay wall EVERYTHING, but after I saw the lack of seak on a cut open and the speed in which you turnaround a mold, I will cut open where ever I can."

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