The When and How of Two Part Molds

Mold making is not always as easy as ABC. But it’s not like rocket science either. You should know when you need to make a mold in more than one simple part and the intricacies involved in the same.

Making a block mold of a model is a simple and straightforward process. However, there are some models that demand two part molds!

Suppose the model has a protrusion – like a mug with a handle. This will make it difficult to remove the model and later the cast from a single piece mold. Or, if the model has a narrow base when compared to the rest of the body – again, extracting the model becomes tricky. In fact, it is just not possible to get the model out of the mold without breaking it apart!

So, why not make the mold in parts itself?

Indeed, multi-part mold making involves making separate parts of the mold that will come together to form a complete mold. The process begins with forming a parting line on the model. This will divide the piece in such a way that the part to be molded does not have any undercuts that will impede its removal from the mold later on. Most times, two mold parts will do; however, intricate shapes may require three or even more parts.

Next you have to cover the mold till the parting line, so that only the part to be cast is visible. This is usually done using clay. While at it, you will also have to mark sprues and keys on the clay surface along the parting line. The sprue forms the opening for pouring in the casting material while the keys are a set of identical protrusions and indentations that will allow the mold halves to align accurately.

Now make the first half of the mold and once set, remove the clay before making a mold of the other half as well. Later, you can easily separate the two parts to reveal the model inside. The two part mold is ready for casting in the material of your choosing.

For more information on the materials and steps for making two part molds, contact EnvironMolds or check out their website,

Uses and Types of Clay

You will be surprised to know that something as simple as clay not only enjoys a broad range of uses, but also comes in a range of variations. The choice obviously depends on the use, so pick accordingly.

The simple and malleable clay is the ideal modeling material for amateurs as well as veteran sculptors. The ease of working and extreme versatility makes clay a popular choice that gives other sophisticated materials like rubbers and resins a run for their money!

Indeed, the use of clay modeling extends across genres – from basic ceramics and pottery to making molds and sculptures to masks, prototypes, special effects and even clay animation.

Different variations of clay are available – there is oil and water-based clay, sulfur and sulfur-free clay and hardening as well as non-drying clay. The choice depends as much on the texture and hardness of the different materials as the potential reproductions of the finished piece. The personal dexterity and preference of the artist also matters here.

For instance, the water-based clays are much softer than the oil ones. But the latter do not dry out or shrink as easily. In fact, the high grade ones are even permanently pliable and can be used over and over again.

The most common uses of clay are sculpting and pottery. Here, the artist usually uses the water-based clays and they are not bothered about the drying as the finished piece will be fired in a kiln to harden it permanently.

However, when an artist is making an initial model for a prop, prototype or prosthetic, they may prefer the oil-based or non-hardening varieties. This allows them a longer window to mold the clay as it will not harden on exposure to air. What’s more, they can even reuse the same clay many times after the casting is done. There is a varying choice of hardness as well to suit different applications.

Most of the clay options contain sulfur and this does not affect the sculpture, mask, prop or prototype as such. The only hindrance is that the sulfur can inhibit the setting of various silicone rubbers. As such, when an artist plans to cast the clay mold in silicone rubber, he has to consider sulfur-free clays.

Apart from these, there is a special type of ballistic clay that is surprisingly handy for testing body armor. This clay simulates animal muscle tissue and can be used as backing for ballistic vests to test the deformations from varying bullet shots.

When it comes to which clay to purchase, the oil-based Roma Plastilina is the first choice of seasoned sculptors for clay modeling. Del Milano plasticine clay is another good variant of the same class, yet less heavy on the pocket. For prototyping and automotive design usage, Chavant offers top quality industrial plasticine clay in both sulfur and sulfur-free variants. Roma Platilina’s ballistic clay is the government-designated backing material for terminal ballistics testing. And if you need moist and self-hardening clays for pottery and ceramics, there are quality offerings from Dresden, Artware and Boneware.