Dopping with Epoxy

by Kathryn on December 22, 2013

in Dopping Techniques

By Dick Walker. Published in FACETS, January 2005

The time-tested method of dopping with hot wax seems to have gone the way of the Dodo bird for most people. I still use hot wax on occasion when I am in a hurry or perhaps someone else is in a hurry. Now I favor the use of epoxy, the five-minute variety. I could use the longer cure variety but it takes a long time for it to become stiff enough to stop running all over the place. Now I use the quick cure epoxy but I use only the epoxy in the tubes, not the kind that comes in the double syringe form. I have found that the double syringe variety becomes a study in madness and frustration.

Why you might ask? Well most of the resins and the hardeners or catalysts are not the same viscosity.  As a result making a proper blob of each is virtually impossible, leaving you with epoxy that will not cure rock hard.

Over the years I have heard of numerous additives used to thicken the epoxy and make it less runny and yield more readily to the solvents used to dissolve it. I have heard of using com starch, corn meal, cream of wheat and cerium oxide, the cheap brown stuff that is. A bit confusing, you bet. I decided to give them all a try to see which method actually was best.

Cornstarch & Epoxy

Cornstarch seemed to be an inexpensive place to start. I prepared a blob of epoxy and proceeded to add an abundance of cornstarch to my blob until it appeared to be sufficiently thick and dopped a stone. After a sufficient wait, I proceeded to facet the pavilion of my stone. After completion of the pavilion I transferred the stone using the same doping method.

Then came the task of removing the first dop so I could cut the crown. I found that the cornstarch epoxy required quite a bit of heat to free the initial dop, enough that it made me just a bit nervous. After completion of the crown again what I felt an inordinate amount of heat was necessary to remove the dop.

Corn Meal & Epoxy

Oh well on to the next filler material. I decided to try com meal this time. I proceeded to mix the com meal with the epoxy as instructed put the stone on the epoxy dop and waited. I do not know what the problem was here but the epoxy failed to harden to my satisfaction. Perhaps some of either the resin or the catalyst was absorbed by the com meal. This was tried again with approximately the same results.

Cream of Wheat & Epoxy

On to cream  of wheat with just about the same results, I may have to juggle the resin catalyst mix a bit.

Cerium Oxide & Epoxy

So on the last suggested filler, cerium oxide. I had tried this filler in the past with satisfactory results but I decided to mix up a batch filling the resin catalyst with enough of the cerium oxide to thicken it sufficiently. This mix hardened quite rapidly with very little tendency to run. After about two hours under a light bulb it was hard enough to commence cutting. When it came time to remove the epoxy from the stone and dop the amount of heat necessary to effect separation was quite satisfactory even for the more heat sensitive stones.

As far as I am concerned the cerium oxide makes the most satisfactory filler for epoxy dopping.

A note on Dops

I have found that the cone dops make a much better base for epoxy dopping than the flat top dops because the epoxy does not work as a thin film adhesive. More mass is required to form a satisfactory bond for dopping. One of the best features of epoxy is that it is waterproof and resists shearing. I have never had a stone come off when dopped carefully with epoxy.

Watch for Humidity

One last thought, one factor that might effect your success with epoxy in general is the humidity in your shop environment. If the humidity is high, as in near a dryer vent or in an utility room, there is a pretty good chance that your efforts to dop with epoxy may result in rubbery or insufficiently rigid epoxy. Make every effort to use epoxy in a warm dry area, for best results.

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