This article is part two of a four-part article on the creation of a full head latex mask. The previous article covered the making of the armature for your clay model, choosing the modeling clay type and selecting the mold making material used to create the mold of the full head clay sculpture. This article will describe how to create the parting line on the head of your sculpture, adding mold keys and then creating the two-part plaster mold.
Creating the Parting Line
Since the full head mask must be cast in its entirety, you will need to make a two-part mold. One part of the plaster mold is used to capture the front of the face detail, while a second half is used to get the impression of the rear of the head. Since this is a two-part mold you must establish a line that separates the two halves, also known as the parting line. The easiest way, providing your design is not overly complicated, is to draw a line staring at the shoulder and running it up over the head, just behind the ear, then over the top of the head through its center and down the other side behind the other ear and across the opposite shoulder. The front half of the mold will be in front of this line and the rear half will be behind it.
Once the line is established the next step is to build a wall on the line about four to five inches high. This wall is used to prevent the mold material you will apply from spilling over onto the other half. The mold material is a casting plaster which you will apply covering the front half of the sculpture to a thickness of three inches. That is why the wall must be up to five inches high, to hold the thick plaster covering back.
The wall can be made from a number of materials, including aluminum shims cut from roof flashing or file cards – both are secured by pushing them into the clay surface. We suggest you use the same clay you used in creating your sculpture. Simply roll one inch thick pieces five inches high and press them on the clay surface along the line that you drew. The clay should be tacky enough to remain in place. Smooth out the clay wall from shoulder to shoulder so that it is straight and without blemishes. This is important as this is the edge where the two halves or your mold will meet.
Adding Mold Keys
In order to assure that the two halves of the mold go back together precisely the way it was removed you must make registration marks. If the mold does not fit together properly, your casting will suffer imperfections and distortions. You must therefore, make certain of a precise fit into mold keys along the clay wall that you just created. An easy way to do this is to begin at one end of the wall using a quarter and press it into the clay about a half-inch up on the wall with a twisting motion until you leave a deep indented dimple or crater. Do the same to the wall of the other shoulder. Then add a third dimple at the top of head, followed by two more halfway between the shoulder and the top of the head on both sides. When you are finished you will have created five mold keys. These indents will produce rounded protrusions on the from half of the cured plaster mold. Those front-half protrusions will lock into the rear half of the mold into a set of mold dimples on the opposite edge, so that you will have absolute registration when you molds are completed.
Creating the Two-Part Plaster Mold
Once you are satisfied with the mold keys, you can begin mixing the mold making plaster. Though you are actually making a mold, this material is actually known as casting plaster, which is available at ceramic stores or on-line. Follow the manufacturer’s mixing directions. Then with a throw away chip brush carefully paint a face coat onto the clay model. This painted coat assures that you have no air bubbles as the effect of brushing will remove them.
Typical casting plaster mixing instructions produce a plaster the consistency of heavy cream, though that is perfect for brushing the plaster onto the clay surface, it must be much thicker for application by hand. So let the plaster mix sit for a while to thicken. You want the plaster to be about the consistency of wet putty. Once it is thick enough, scoop it up by hand and apply it to the front half of your sculpture. It needs to be applied three inches thick. As you add the plaster you can dip your hands in water to help smooth the surface.
Allow the plaster mold to dry overnight. Then it is time to remove the clay parting wall and discard it. Clean up any clay left behind on the plaster edge. You need to apply a release agent to the plaster edge and about two inches over it on the top surface of the plaster mold. Use petroleum jelly for this purpose and liberally apply to the plaster.
Once the petroleum jelly has been applied you can mix the mold plaster and apply it to the rear the same way you did on the front – first a face coat, then a thicker application of three inches. One that is smoothed out, the plaster mold process is complete. It only needs to set overnight before it is ready to be de-molded.
Part 3 of Creating a Full Head Latex Mask will teach pouring of the latex casting materials, curing the mask, de-molding and trimming
Part 4 of Creating a Full Head Latex Mask will teach painting and finishing.
Post time: 04-15-2017