Mold Making - Initial Layup p. 2


        The hands/arms were removed from the original to ease making the mold and ultimately to make removal of the wax from the mold easier.  After removal of any pieces (for reasons just given), all parts are given 2 coats of Varnish (I use Bullseye Varnish in spray cans and also “bulk” from a “finish” sprayer).  I do this for two reasons.  1)  to give the clay of the master a skin, that is relatively hard, which is good to have when pushing the molding clay up to the clay (master), so it is less likely to be dented/damaged while you are “working against it” pushing the mold clay tightly against the master, and 2) the solvents used in the release to be applied, do not get to the clay master and potentially soften it.  I normally apply a release to the piece after the Varnish, to allow for easier clay removal from the master/Varnish coating.  Which release to use will vary depending on which RTV you are going to use (this is important to read!!!) and there is discussion about this here

        The front and rear legs of the master, removed and molded separately to make removal of the wax from the larger, main piece to be molded, MUCH easier and the mold making easier (legs in the second picture below). 

        I have the hands/arms and peace pipe parts laid out inside the clay “damn”.  These pieces would normally be imbedded in a soft/very soft sulfur free clay (I like Chavent and I get it from Douglas and Sturgess in San Francisco, CA) and the clay would be carefully worked up against the “piece” to “make” the separation of the 2 part mold we are making.  There are numerous tools I use to do this clay work, some of my favorite and where you can get them are on this page

        So once you get the piece(s) set into a base of clay, you need to add clay from the “outside” of the mold to the clay/master pieces so there is a way to get wax into the mold cavity once the mold is finished and being used.  I use a different color of clay to make a “pour tube” (see the reddish brown clay going from the “top” of the legs to the edge of the gray clay, in the second picture below?) for this, so I am sure to leave them in place when I get the first side of the mold finished and start working on the second side.  If there are areas of the piece being molded which might create a problem with air capture and thus poor or no fill with wax, some form of air venting is needed and now is the time to put it in place.  It is difficult to see, but in the 3rd photo, see the red lines right next to the clay of the original?  This is wax wire pushed into the “ground” clay (just over 1/2 way), placed close to the clay master, so if air vents are needed once the mold is finished, the vents can be cut into the mold rubber from the master clay/void, over to the “wax” groove left in the rubber mold once the mold is finished and the wax wire is removed.   The wax wire end is run to the edge of the mold so the air can get out as needed.  Many RTV rubbers are so close fitting that there is no place for air to get out other than thru the pour hole, this can blow hot wax back on you, or these vents.

        I like mold alignment buttons in my molds, especially if the mold is rather flat, to assure that the 2 halves are aligned properly when put together.  I use the “barrel” end of a Sharpie pen to make smooth tapered indents into the clay (see picture 1 on pg. 4).  I place them about every 1” or 1.5 inches all around the piece, outside of the wax wire (it I have used it for the air venting).

        Before applying any RTV, I spray the “clay up” with release (Teflon for Silicon RTV or  silicon or universal release for most other RTV rubbers).   Once released, carefully apply the initial layer of RTV making sure it gets into all detail and all areas (you can “blow” it in CAREFULLY with compressed air or carefully use a brush), working the air bubbles to an edge of the RTV, then CAREFULLY spread the rubber to get an even coat.  The first coat is NOT thickened so as to make it easier to get it into the detail.  Once set up (don’t wait too long or the next coat may not adhere to the previous coat - this is important to remember so your molds don’t delaminate later on) apply the 2nd coat.  The second and third coats can be thickened with what ever thickener your particular RTV requires or that you are using.  Once set up it is time to apply the mother mold.

See the reddish lines next to the brown clay parts?  This is red wax “wire” pushed into the clay that will make air vents in the rubber that can be cut to to bleed air if needed.

Legs with “fill holes”, reddish clay pieces laying on gray clay base, then more clay is put down and worked against the clay master parts to make the first side of the mold.  “Walls” need to be added yet.

Layout of pieces in preparation of laying down a “bottom sheet” of clay b4 building up the sides to the parts to make the “1st” half of the mold.  Still needed are the clay pieces to get the wax into the parts and any air vents.