Making Micarta Scale Material
Since many of you on SRP expressed an interest in Micarta as a material from which to make razor scales, I have made time to properly document and illustrate the process.
Micarta is really nothing more than a composite of cloth or paper in glue. Long ago the material was originally made with phenolic glue, but for our purposes epoxy resin is more convenient.
Almost any cloth should work, although my preference is for simple woven cloth from natural fibers such as cotton, linen or silk. In my opinion, stretch fabrics are probably less interesting as they might contribute to the finished Micarta sheet being somewhat too flexible. The reason for my choosing a cloth made from natural fibers is simply from a fear that some sort of chemical reaction between the epoxy resin and synthetic fibers could end up making for a weak result. Another cloth material that could be used is fiberglass. Structurally it is excellent and is totally compatible with epoxy resins. I just don’t think that fiberglass is so very pretty for the purpose of making decorative razor scales.
Paper may also be used within the composite, but one must take care that the paper is sufficiently porous to fully absorb whatever resin you use. If you chose to use some paper with a plasticized upper surface (inkjet photo papers, for example) it is possible that the plasticized surface would not allow the resin to permeate sufficiently and that the resulting piece of Micarta might later come apart, shearing along the (insufficiently impregnated) inner paper surface. This is definitely not desired.
Do be aware that cloth or paper will no longer appear the same once drenched in resin. This is somewhat akin to the way that clothing changes appearance when wet. Most usually, colors become darker and somewhat less brilliant. Additionally, some measure of opacity is lost. Paper, even more so than cloth, may take on a very different look when wet than when in the normal dry condition. The rule is: If there is any doubt, experiment on a small sample first before committing your time and materials to a finished product.
We are choosing for epoxy resin as the glue to bind our Micarta. However, there are many epoxy formulations and not all of them are equally suited to our purposes.
The correct epoxy should first and foremost have a slow set and a relatively long ‘working time’.
The ‘working time’ is that amount of time between first mixing the resin components together and when the mixture starts to ‘gel’ (thicken). An epoxy resin with a long working time is what we want, since we are going to carefully apply it to each layer of cloth in our lay-up.
The ‘setting time’ (also known as the ‘curing time’) is that amount of time it takes the resin to harden to the point where it can be safely handled and/or used. In general, an epoxy with a long working time will have a long setting time. Do please note that once the usual setting time has elapsed your epoxy will have a reasonable hardness, but that in some cases the absolute hardness of the epoxy resin will only be reached after some additional time has passed (hours or even days). This varies from epoxy to epoxy and so one will want to consult the technical information sheet for the particular formulation one is using.
We are also looking for an epoxy which does not exhibit a strong color influence on the final result. Again, in this regard, not all epoxy formulations are the same. For many industrial purposes, color and or transparency may be of no importance at all when compared to other more important qualities such as strength, water resistance, heat resistance and so on.
I am fortunate that the epoxy formulation I am using is rather good in all the aspects that pertain to the hand lay-up of Micarta sheets. This epoxy formulation is intended for pour-surfacing of floors and table tops. Although each of the two components have a bit of color on their own, when mixed together they become water clear. The working time is something like twenty to twenty-five minutes (20-25 minutes) and the setting time is about twenty-four hours (24 hours). During the working time, the consistency of the mixture begins by being only slightly thicker than milk, becoming rather more like syrup near the end of the working time. As a final benefit, this epoxy formulation has the quality of filtering out UV rays. This should offer a measure of additional protection against color aging of any cloth or paper within the matrix of my Micarta.
A few words about temperature are in order at this point. A minimum amount of heat is a requirement for epoxy resins to set. Most curing times (setting times) are expressed as the amount of time required for the mixture to harden when at room temperature (20°C = 68°F). If one lowers the room temperature, the setting time will be increased. Lower the temperature too much and the required chemical reaction will slow to the point where the epoxy will fail to cure. Extra heat (increased temperature), on the other hand, will accelerate the chemical reaction, thus reducing the setting time.
The chemical reaction that enables Epoxy resins to harden is exothermic. ‘Exothermic’ is a fancy way of saying that the chemical reaction generates heat. The larger the mass of the curing epoxy, the more heat that tends to collect. And, since increased heat tends to generally accelerate the setting time of epoxy, it can be that both the working time and the setting time will be reduced if that heat is allowed to build up. Some hobbyists have reported this effect when mixing up large batches of resin. In practical terms this can mean that the rate of hardening can accelerate such that the mixture hardens while you are still trying to apply it. In the small amounts and the thin layerings of epoxy which we will be using for creating scale material this should not be a problem. Just remember to stay away from the extremes of heat and cold when using epoxy resins.