HO Studley

Replicating Studley’s Alcove Arch, Part 2 – Casting the Duplicate


Once the wax model is refined to an acceptable point the time has come to make the rubber mold for casting the replica.  I simply lay the wax model down on a bed of sulfur-free plasticine clay, which is necessary to seal the back side of the model and prevent the rubber from seeping underneath when the rubber is poured in to make the mold.  If it does seep in that is not the end of the world, it just makes more work in extracting the model and refining the rubber mold.  What IS the end of the world for this process is to use any sulfur-containing modeling clay instead of the sulfur-free plasticine.  The sulfur in the modeling clay inhibits the chemical reaction in vulcanizing the rubber mold, and in the end all you have is a gooey mess that never makes the transition from liquid to solid.  Believe me, you do not want to enter this territory.

With the wax maquette set down on the plasticine, I build a dam around the space with Logo blocks or some analog.  It is a simple and cheap way to enable a near infinite multitude of sizes and shapes for making molds.


Once everything is ready to go, I mix the silicone rubber and pour it in.  For many years I have used products from Polytek; their prices are good, the product is good, but their customer service and technical help are stupendously great.  Colleagues of mine are partial to Smooth-On products, and I have seen excellent results with their products but do not have personal experience with them.

I like to pour the liquid RTV silicone in a fairly thin stream from a foot or more in height.  This breaks up almost all of the little bubbles that become included in the cup when stirring up the mixture, and bubbles are the enemy.  By pouring in this manner, starting in one corner of the mold form and letting it flow over the model of its own accord, I find virtually all bubble problems disappear.


Once I have a rubber mold I find acceptable, and this often takes several generations of models and subsequent molds, I’m ready to cast a replica.


For these arches, I found that using West System epoxy worked just fine, and I mixed a paper cup with the resin and hardener, along with a dollup of black powder pigment to replicate the ebony of the original.  I also dusted the surfaces of the mold with the same powdered pigment, to assure a “not glossy” final surface and to help reduce any surface bubbles, always an issue when casting heavy bodied resins.


For these arches I had the added element of including a pearl button in the element where Studley marked the center of the arch.  I had the best luck with this in putting a drop of the resin in the recess then placing the button, using the liquid resin to hold the button in the correct place.


Having the button move while pouring the resin is a constant problem, I can only conclude that the specific gravity of the pearl button and the casting resin are similar, causing the button to “float” a bit after the resin is poured.  Waiting a bit on the full pour after the button is placed and the resin begins to increase in viscosity helped but I am still wrestling with perfection on this one.

I take the raw casting out the following day, and smooth the back side on a flat  plate with sandpaper, and the replica is done.



I prepared a panel with several of the decorative element replicas from the Studley Tool Cabinet (this picture is just a mock-up, the best castings were not yet ready when I took it), and if you make it to the exhibit next week you will get to handle that panel.

There are still plenty of tickets for Sunday afternoon especially, I think the remaining time slots are getting full or nearly so.  If you are willing to hang around until Sunday afternoon, you might have a darned near private viewing.

See you next week.