Modeling in Wax & Clay
with Latex Molds

2010-03-21 (Assembly from earlier parts) Rev. 2010-03-23, -07-22, -08-14, -10-24, 2011-11-12,
2012-01-15, -08-17, -09-19, -10-12

Return to Sitemap

Local Links
Intro My Work Method
Clay & Clays Casting Wax
Modeling Clay Clay Modeling
Latex Molding Compound Latex to make small face
and head mold
Two sided molding Small Plaster mold example
Mixing Plaster (new page) Casting Methods
Sculpture Development
Related pages
Metal Center
Mold Center
INTRO- This page was created from sections on other pages to bring together the tools, techniques, and materials for modeling in clay and wax and using latex molding compound to make copies which might then be combined.  In most cases the items made are on the other pages with links from here.
Mold preparation for small moldsI normally work by making a soft clay model such as the dark blue one at right of Washington's profile from the coin .
 From this I make a latex mold like the one below the clay model or the Lincoln head still encased in latex to the right.  In both cases, the latex is soft and thin enough that it requires a plaster backing so it won't distort. The support for the Washington is under the latex while the recently removed Lincoln backing (see the white powder on the latex) is to the lower right. 
  My most common use of these molds has been wax copies of the model as shown below and on other pages, although these two small molds were used to make sulphides.  The molds have also been used to make plaster and investment copies. One of my techniques is to make 1/3 models, make 3 copies, then assemble to make a lost wax original for metal casting.
Goblet casting wax - 3 hands, 3 feet - view 2 The image at right shows one result - a clay model of hand was built on a curved plaster shape set in a V trough.  The model was coated repeatedly with latex molding compound to form a flexible layer.  This was backed with plaster that extended down to the support.  The mold was separated from the clay then the two plaster parts were fitted together around the latex and casting wax poured in.  This was repeated three times and the three copies were assembled as shown along with copies of feet to make a goblet stem. The general processes are shown below and the making of the goblet is here. 2010-07-22
Clay these days refers to any material that can be molded into shape and stay there. The material can be paper, earth, plastic, or dough. Although sand, plaster and cement/mortar mix can be made stiff enough to mold, they are normally not used this way and are not called clay.  In the past, the word clay by itself always referred to a material from the ground created by natural weathering of certain minerals. This clay consists of flat platelets that when wetted down will slide past each other but still adhere and hold the new position. Usually the clay must be fired in a kiln at high temperature (1800F or more) to convert part of it to a glassy substance (vitrify it) for it to have permanent strength. Just drying it will produce a weak object that will soften if it gets wet. 2012-10-12
Modeling clay thus referred to earth clay moistened with oil and wax rather than water. Long used in gray, white or dark green in large quantities for the original of bronze and other sculptures as well as full sized car concepts, it is now available in many colors as it is used for claymation - the animation of figures in 3D for photography where the position can be modified for each frame - Gumby, etc.
Air dry clay usually refers to earth clay with added binders added to give it strength and avoid dusty surfaces when dried. Normally, air dry clay will soften if gotten wet. Some air dry clays can be fired at low kiln temperatures (04) making them more permanent.
Paper clay is one of two materials. The more obvious one is finely ground paper that forms an air dry clay of very smooth consistency that can be carved like wood and is popular for models of dolls.  The other one is an earth clay/paper mix that is easy to work and results in a lighter clay object. The paper burns out on firing.
Polymer clay is finely ground plastic in a solvent binder that is baked at about 275F to form hard PVC plastic objects. It works easily and is brightly colored and is very popular for small projects like charms, in part because it is fairly expensive. Polymer clay is very sensitive to overheating and will give off noxious fumes, including chlorine, as well as darkening.
Recently, companies apparently can't define their product as clay without calling it modeling clay even though it also has another good  adjective - so we see paper modeling clay, air-dry modeling clay, polymer modeling clay.


Modeling Clay is a never hardening earth clay mixture that is moistened with oil instead of water.  The clay is a very fine powder without grit.  I recently (2010-03-22) learned from here that the formula also includes a grease and a wax to control hardness.  I buy mine in blocks about the size of a pound of butter - that weigh two pounds - from artist supply places, but it is sold in that form in some craft stores and in sticks of various colors shaped like quarter pound sticks of butter/margarine in craft stores, toy stores, and school aisles of grocery stores. With the rise of home digital animation, it is more easily available in small quantities of bright colors for claymation (Gumby).  Plasticine is a brand name, as is Plastina.  On a more serious level, the clay is used in large amounts for making the originals of bronze castings and car models during the design process. 

Tools for working clay and wax, green waxClay tools and Tupperware carrier

Clay working tool made from brass sheet for convenienceModeling clay is generally soft enough to work with any handy tool, including fingernails.  On the plate are legitimate wood and metal tipped clay tools sold for pottery clay, a chop stick, and dental picks sold in hardware stores.  Shown on the oval container and in the large image is of a 2" square of 1/32" brass cut to various angles - all the edges rounded. It was partly made to go on a plane before requirements got so stiff but also to fit conveniently in the plastic container with some clay and mounting disks  for small work as shown below. 2010-01-17

This soft clay model was then used to make a plaster mold in the halves of a small plastic bottle using standard clay mold techniques. (i.e. support the model so the plaster will come to the centerline of the model, pour plaster and set; treat the surface with English soap as a release, add the other half mold, cover the rest of the model, set and unmold.)


Latex mold building compound as used below and here is most commonly available at craft and hardware stores in a plastic 16 ounce package like that shown.  Other sizes up to a gallon in this brand and in other brands up to five gallons are available.  Inside is a thick white cream that is natural latex (originally tree sap from rubber trees) preserved with ammonia.  When the ammonia evaporates the compound turns amber as shown below.
A factor in using it is that it can not be applied too thick because the surface sets and prevents the mass below from setting.  Air flow and especially warm air flow speeds drying, so a layout works well with a small fan blowing on the project with a return every 15 minutes or so to paint another layer.  Brushes must be cleaned with soap and water before the rubber sets in them.
An alternative, which is used when making masks, it to have a plaster mold or model.  As with clay, the dry plaster pulls water out of the latex and allows it to cure.  This PDF document from a latex vendor gives good instructions for working this way. 2012-09-19

Latex rubber is moderately strong in terms of peeling it off the model, but is structurally weak.  The company shows making molds of upright objects by flaring the base and then casting by supporting the mold by the flange upside down in a hole in a cardboard box.  For the kinds of molding I do, it is much faster and accurate to apply a plaster shell to the back of the latex mold while still on the model.  In cases where there is a core or mount for the model, as just below, fitting the shell to the mount permits pouring wax between two which would be much more of a problem with a full surround mold or and open mold where the result would have to be heavily trimmed. 
When latex is covered with plaster or used to mold plaster, the water in the plaster makes the amber mold turn a foggy white and it is somewhat weaker.  The water evaporates and the amber color return. 2009-08-02 
The entire process is also shown on car-body-mold.htm with the lighter color damp latex; the object there being to make a mold for pressing polymer clay to make a plastic model. 2012-08-17
The book The Prop Builder's Molding & Casting Handbook by Thurston James [almost all of which can be read at this link] says that latex can be preserved from aging by chemicals in the atmosphere by using Armorall, sold for tires and dashboards, etc. 2009-12-18
Knowledgeable people will notice that I don't mention silicone molding materials.  That is because I have not used them and they are fairly expensive.  As normally used they are more self supporting and are more durable than latex molds but are sensitive to sulfur in materials which prevents setting.  Places discussing it suggest using slow drying water based clay or (link) carefully testing the oil based clay or using a specific brand of silicone compound.  2009-12-18                                                              Top
Head mold for casting investment This sequence shows the steps in building a mold on a model.  In this case to cast investment on which wax will be built to make either a goblet or sculpture with glass blown inside an outline structure.  My thoughts on the structure have been in two directions: a medieval knight type helmet or a brass structure like the highlights on the face with glass becoming the skin and recesses in between.
 Since this was not to be a realistic representation of a particular person, I chose to be very bold.  The core is a wooden egg with features built with white Sculpy.  As is usual, pieces of tag board are inserted on the midline of the halves of the mold.  Latex rubber is applied, forming a good flange.  If the rubber is applied in thin layers and air flow is provided, it dries fairly quickly.  The mold material  packaging calls for 10-20 layers.  This works if you have a lot of time to brush on the layers and clean the brushes. [Other materials that cost more, like silicone rubber, mix up and set chemically so one thick application may be possible.]
 Brushing thin layers is important at the beginning no matter what if there is small detail to avoid bubbles.  If the mold material is swabbed on thick, it is vital to let it dry until all the original white color has changed to amber.  In thick areas like the ear or eye socket on this model, it may take a day, even with air flow, to set all the rubber.  But if it is convenient to pay attention once or twice a day - like on the dining room table at breakfast and dinner.  What I do is apply it further to the thin areas, whiter in this case, so the mold is stronger and will not tear.
  The right picture in the center row shows selective application.  Experience guides how thick to make the rubber.  Usually if it is off white in the thinnest it is probably strong enough.  The lowest row shows the second side being prepared for pouring plaster, the first side having been done.  The purpose of the plaster is to support the flexible rubber to prevent distortion.  With a smaller mold, it can be supported at the flange.  I make the plaster fairly thick, which has to be poured fairly quickly. 2005-04-18

Mold preparation for small moldsThe picture to right shows the steps I use in making flat molds for sulphides and glass while showing the general process.  More images of variations are shown here.  I bought the wooden disks at Hobby Lobby or Michaels.  Using either plastic clay or Sculpey, I build up the image, like the profile of Washington taken from the coin, often while riding or waiting for the bus, with the detail work being done at a table. See sample tools above.  Then thin layers of molding latex are painted on, also making a flange onto the wood surface.  Avoid the temptation to put on a thick layer, which takes much, much longer to set than many thin layers, even if cleaning the brush is a nuisance.
  Before the clay model is removed, I make an aluminum foil cup around the bottom of a glass and set the disk in it so that I can put plaster of Paris neatly over the disk. [Mixing Plaster] The purpose of the plaster is to support the latex mold when wax or investment is poured in.  The shell mold looks like the lower left on top of its support.  To the lower right is the support for the head (Lincoln) above it.
  The mold can the used with casting wax or investment.  If the wax is used, the result is covered with investment, the wax melted and burned out, and the hole filled with glass or metal, as making the dog and cat heads here.  If investment is used, then it is encased in wax in shape of metal, which is then further invested to allow casting a mold like those shown above. 2004-07-05 Storage Note

Head mold (both sides) and supportHaving worked on the clay face for the bottle mold this montage illustrates the pieces and two sides of the latex mold - interior above, exterior below.  Through a curious optical illusion, the interior mold seems to bulge out at us.  The plaster keeps the latex from distorting under the weight of investment and heat of melted wax. The lower image shows how the latex turns white when kept moist - in this case from the plaster backing.  It is weaker in this condition, but dries out and strengthens again, turning a uniform amber.  Notice that not enough plaster was piled on, so there is a hole where it was thin over the nose. 2005-05-01.

Storage Note: I now strongly recommend that if a latex mold is to be kept, a plaster copy be made in it and dried and then returned to the mold to preserve the inner shape.  Also, as you might expect, the mold will survive longer at cool dry room temperatures than at hot or moist conditions. 2010-10-24


Casting wax is amazing. It is unlike any candle or paraffin wax I had handled previously. First it is very tough and flexible, so once built, a mold will take considerable handling. Ironically, it is not very waxy - not slippery or hard to hold. It can be poured to make sheets, cast in plaster slots to make rods or flats, cast in plaster or rubber molds to make components and, perhaps most importantly, welded with a heated blade to assemble pieces and carve or repair shapes. 2001-10-09 

A wax model can be built up by making separate pieces, including by casting, and applying to a base unit and by using various rod and flat sheet shapes to provide pattern and structure.  Jewelry supply places, such as Roseco, offer a huge number of basic ring shapes, tubes with ring profiles to slice off, broach/badge/buckle designs, and molded add-on decorations as well as thin and thick rods, sheets and tubes in various hardnesses.  Operating cheaply, I buy bulk wax that comes in small pellets and mold my own.

I have made plaster flats with grooves from clay rolls in them and cans with tubes through them to make round wax sprues.  Melting wax over water in a bread pan and letting it cool produces a very nice flat slab for cutting.  Pouring wax onto water does not work well.  Microcrystalline wax is called that because it has finer crystals/flakes than paraffin waxes: 2010-03-22

Make a pattern of the piece in wax, pour investment around it, and go (well almost, see here.)


Alcohol lamp for heating tools for wax. WAX TOOLS - Certain hard waxes can be carved with hand rasps and rotary tools, but the medium wax I had purchased flexed some and resisted easy cutting - heated tools were called for.  Commercial heated loop and flat tools are available but I started by using a thin flexible spatula sold for spreading frosting on cakes to cut into and melt away parts of the wax. Bits of wax can be melted on the surface for adding wax to a surface or filling cracks.
 For a while I did my wax working using an alcohol lamp for heating metal blades and spatulas.  This is nice because it gives a flame that is wide and does not easily heat the blades to the point of damage while giving a variable control of temp and thus melting on the tool. The lamp shown has a thick wick and a faceted base so it will sit upright or tilt as shown.  Despite the cap, alcohol can not be stored in it between uses - it leaks or evaporates. The soft flame is very nice for controlled heating.  It is less nice because it cools quickly when used to melt into a wax casting.
Wax tools and dimmer So I rigged a dimmer to plug in a soldering iron, turning it up or down as needed.  Full temp smokes and melts the wax too fast.  This is nice for constant controlled heat but doesn't allow "feathering" - melting some wax and then pulling and chilling it in place like with the alcohol flame heating.  I am going to/did make a metal blade to replace a tip on the soldering iron and see if it gives more variability. Little soldering irons with fine tips are sold for sculpting the wax, for way too much money. Roseco 2005-05-23  The box shown is made of pieces available at hardware store electrical departments, but actually came from my miscellaneous junk drawer, and includes a plastic outdoor surface mount 4x4" box, a switch/outlet cover plate, a brown outlet, a cheap dimmer, and a short cord.  The dimmer can handle to 600 watts, but the soldering irons are 30-60 watts.  The dimmer knob is marked to permit resetting to good points found by trial and error. [Wiring is simple - one cord wire to silver screw on outlet, other to either dimmer wire/screw then connect other dimmer wire/screw to gold outlet screw. 2011-11-12]
  Some small soldering irons mount their tips by having a thread on the end and an inside threaded cup on each tip, but both of the soldering irons shown use a set screw to hold the tip, which is basically a 1/4" rod, which allows much easier/cheaper making of new tips.  The one on the right has a home-made tip of rod with a slot cut across it with a narrow sheet of brass silver soldered into it to make a heated spatula.  The device to the right is a first experiment at a heated tube for extruding slender wax rods. The rod that fits in the soldering iron projects up and left, the extrusion tube down and left and the feed tube with a wood pusher up and right. 2007-06-04  
I needed to cut holes in the wax shell, so cross drilled a 1/2" thin brass tube for 1/4" thick wall brass and soldered them together by installing in the iron and running it on high.  Not only cuts holes with end, but scoops excess inside wax. 2007-09-07
Goblet casting wax - 3 hands, 3 feet - view 2Wax welding is done by heating both surfaces, over the flame and/or with a flat heated tool and then pushing the two together.  The flat tool can then be used to further melt selectively by sliding it into open places or by melting small bits of wax on the tool and tilting it to deliver wax locally.  The join can be smoothed with the same tool.
One of my techniques is to make a third of the final design in modeling clay in a V-trough, make a mold of that, make 3 copies of the section in wax and weld them together, as in this wax model also shown in selected image at right.
Wax forming using a glass plate set on screw heads to adjust.In a more prosaic use of wax casting and welding, I wanted to make both flat and tapered wax slabs for assembly of items like the box form shown at right.
One way to make thin or thick flat slabs is to melt wax on water and let it cool there - which I do in my annealer/kiln, most commonly using an old bread pan.  Pouring melted wax on water does not work well - the bottom is all pebbled.  A slight problem is cutting the slab out of the pan - it tends to fasten to the walls.
I wanted to make this shape to make some plaster holes. I considered the problems of cutting the side slabs to exactly the same end angle and decided I would rather assemble tapering wax to square end side pieces.
So I conceived the idea of pouring wax onto an oiled glass surface that was tilted.  Partly this came from having casually made thin puddle slabs, dots, and strings by dribbling wax onto wet plastic or glass for use in building models.  For no good reason, I had on hand a 1/2" square steel bar which I cut into four equal pieces and an odd piece of 1/4" plate glass - which I made safer by hitting the edges with a sharpening stone. I set the glass plate on the heads of three sheet metal screws put in a plywood plate, which allowed me to level or tilt the glass as desired.  The four steel bars can frame a rectangle up to their length, as shown.  Flat slabs can be made much more quickly than with the water method because there is much less time for heating and cooling.  I melt wax in a pot taken from a popcorn popping cart put out for junk, but I had planned on using a Fry Daddy pot. The same dimmer unit used with soldering irons is used to control the pot temperature. 2010-03-23 Wax melting pot using old popcorn popper pot.

Investment and plaster working information once here, moved to Goblet Casting

Below are two versions of tappers made for breaking thick glass to illustrate other molding steps.

Tapper head - clay model, plaster mold, wax for investmentTop center is the clay original, then the two part plaster mold used for casting the lead, and wax cast from mold, sprued for better brass casting, not yet cast. 2008-01-12 In the next image the upper one was cast in lead in plaster from the modeling clay original. It was drilled for the handle after casting.
The plaster shows the common technique for molding when the shape permits pulling the mold straight off in sections.  The right disk was made by having a shallow cup of wet plaster and the small clay model was pushed half way in and held until set. Two indentations were carved and the surface treated with separator.  Another small batch of plaster was poured on top and when it was set, the two halves were pried apart and the clay taken out, with some plaster adhering as shown.  A channel was cut in each half to allow pouring in lead or wax. Wax can go in damp plaster, but the plaster must be completely dry for lead casting to avoid a steam explosion or bubbling through the lead.
Cast glass tappers in lead and brassThe lower one was cast by building up casting wax on a stick by dipping in molten wax and smoothing.  The stick hole was used for mounting a small hole venting for investment to enter the mold.  A poor porous casting but not so bad that the black line is a crack but a marker line to guide to a smooth part for tapping.  As shown right, the plaster has been used to make a wax for an invested lost wax casting with proper spruing. 2008-01-06

Sculpture Development (answer to a question)
Because it is hard to carry around sculpture materials - heavy, messy - most sculptures start with sketches in notebooks. Most sculptors probably begin working in modeling clay - oil moistened earth clay that never hardens - to be able to develop and modify their ideas. Small models can be built without structure, but bigger and ones with thin support (legs, etc) need a metal armature.
Permanent versions of the sculpture are made by pulling molds and casting plaster or wax for lost wax casting of metal, plastic, plaster, or glass. Or the modeling clay version is used as a model for the artist or professional craftsmen to point up and carve marble, wood, plaster, or other materials.
The artist provides ongoing control of the sculpture including paint, patina, and surface finishing of the almost done product. 2012-01-15


How many metal casting methods are there?
Half a dozen?
Die casting is done with lower melting point metals and involves a metal die into which the metal is forced - like plastic injection molding. Metal bodied electric tool cases like hand drills and kitchen mixers are made this way.
Simple pour molding into reusable molds is done with low melting point metals up to aluminum. Short run toys for example, lead soldiers, bullets for home reloading.
Simple pour molding into non-reusable molds - aluminum into sand molds for making address plaques, etc. is done this way.
Enclosed sand casting with poured metal with two or more part molds and perhaps cores, venting and sprues to get the metal in. Iron/steel/aluminum engine blocks. Heavy duty basic castings for construction equipment - further machining being done for bearing mounts, etc.
Lost wax casting with solid investment - rings, fine art. Bronze, brass, silver, gold. Mold is heated to melt out the wax and set the investment which is then chipped away from the poured metal.
Lost wax casting with ceramic investment - wax is dipped in liquid then silica flour and then back and forth to build up a thick coating - a dewaxing oven burns out the wax and fuses the silica to a hard shell into which, while still hot, the metal is poured, the shell then being chipped/blasted off.
Lost wax casting with sling molding - a single item mold is made up usually with investment and is heated and mounted on an arm in a device which has a place for melting metal with a torch, a heavy spring drives the mold arm in a circle and the metal is released to forcefully fill the mold like injection casting but with much higher temperature metals, up to platinum in jewelry making. 2012-01-15

Back to Site Map

Contact Mike Firth