Making the 2nd Side of the Mold p. 4


       Remove the clay that the mold rubber was brushed against when making the first side of the mold, but try to leave the clay that creates the outer “dam” (see 1st photo below, it is the gray clay at the outer edge of the mold).

        See the “buttons” all around the piece in the first picture (the raised buttons that have some clay stuck on them as they were not well released after making the indents into the clay)?  These are the alignment buttons that were made with the Sharpie pen barrel.  These are the positive or “out” part of the button.  When you put on this 2nd side, you will make the “negative” part of the button so that they will align the mold when you put the 2 (or more) pieces together. 

        The clay should come off of everything pretty cleanly if things have been properly released.  In the pictures below, a Urethane RTV was used and it LOVES to stick to most ANYTHING it come in contact with, so if you are using a Urethane, BE SURE TO USE A GOOD RELEASE AND BE SURE EVERYTHING and I mean EVERYTHING that the Urethane RTV is going to come in contact with is well released, otherwise this particular variety of RTV is a very good glue!!!  HOWEVER, Urethane WILL NOT stick to itself if a new coat is applied to a previous coat that is relatively well cured (more than a few hours old).  Remember this because applying a new layer of Urethane to an old, well cured surface layer of Urethane WILL most likely cause the new layer to ultimately delaminate from the old layer.  If you need to add a new layer to an old, well cured layer, contact your mold material supplier for a product that will assist getting a better old to new layer bond (Douglass and Sturgess in San Francisco/San Leandro CA is my main mold materials supplier). 

       If using a silicon, there is very little that it will stick to, except itself, unless the previous silicon layer fully cured, then it will not stick to itself well and most likely will delaminate, so again, contact your mold material supplier to get a product that will give you a better bond (Douglass and Sturgess in San Francisco/San Leandro CA is my main mold materials supplier).

       Once the mold is cleaned off of any clay needing to be removed, make the outer wall for the second half of the mold.  This can be put on the exposed part of the clay that was left on from the first side of the mold (the outer “wall”) and the seam between the new and old “walls” worked together to make a connection and to keep any mold material from leaking out between the 2 parts.

        So now you have the wall built for the second half of the mold.  If using Urethane, be sure to coat the parts of the exposed mold rubber of the first side with a release which is often/usually silicon based.  If you are using Silicon RTV use a Teflon release as a silicon based release will most likely act as a glue, not what you want.  Be sure to apply release or you may end up making a one piece mold which will be no good.  Lay down the first coat and “blow” or carefully brush the RTV into all of the detail.  Once it is set up, the second, slightly thickened coat should be applied and once this is set up, the 3rd, thicker coat can be applied.  Then apply the mother and when it is set up, you are now ready to take the mold apart and remove the “master” (usually overnight curing is good, especially if you are using a lamp or other mild heat source to speed up the cure of the rubber). 

        When taking a mold apart for the first time, sometimes there will be clay, varnish or other materials from the master stuck to the RTV.  Wash with hot soapy water or if needed use a thinner or cleaner to remove this material (test what ever cleaner or thinner you are going to use on the outside of the mold RTV to make sure it does not react with or dissolve the RTV before using it on the inside).  You can also make a “waste” wax to “clean” this unwanted material from the mold.  If you have used Urethane or most any of the other RTV type rubbers, release the mold surfaces before putting the mold back together in preparation of casting a wax.  I release even silicon molds but normally only for the first wax.

        For wax casting, Urethane materials need to be released each time you use them.  Silicon does not need to be released for wax casting but it is fine if you choose to release it.  Other RTV’s will also need to be released.