If you ask ten different watch manufacturers about their recommended protocol for using epilame in the servicing of a watch, you are likely to get ten different answers; even among watch brands that operate under the same parent organization. Technical documentation from one company will recommend applying epilame to components X, Y, and Z, while another will specify just X, and yet another X, Y, Z, and Q. Recommendations on how the epilame is applied, for how long, and whether it is left to dry on its own or under a flow of warm air also vary from company to company.
This latter point of divergence is one I’ll take sides on. It is critically important that all metal components of a watch that have been treated with epilame be dried under a current of warm air. I would say that it is equal in importance to keeping a movement free from fingerprints. Just as the natural oil from our hands can encourage corrosion, and also draw lubrication away from its intended functioning surface through capillary action, so too can epilame induce corrosion, while the absence of epilame can result in lubrication being drawn away from its intended point of action.
Epilame is a surface treatment that smooths out microscopic imperfections in the surface of a material, similar to the way that a snow or skateboarder uses wax to smooth the surface of their board or rail. Traditionally, the acting medium in epilame was, actually, a wax-like substance known as stearic acid. The modern equivalent of stearic acid is fluoropolyester, which is suspended in a perfluorohexane solvent. When this mixture, in a ratio of approximately 1 part fluoropolyester to 100 parts perfluorohexane, is applied to a surface, the perfluorohexane evaporates rapidly, leaving behind a nanoscopic film of fluoropolyester. The combination works great. However, the reaction between the perfluorohexane and the surrounding atmosphere that causes it to evaporate so quickly is endothermic, meaning that it draws energy in from the surrounding environment, resulting in cooler surface temperature upon which humidity in the atmosphere can condense. If the relative humidity at the time that the epilame is applied is high enough, moisture from the air will become trapped in the surface of the metal and can result in a buildup of corrosion over time. So, to prevent this from happening, the freshly epilamed parts should be warmed to just above room temperature as the perfluorohexane evaporates.
If such precaution isn’t taken, the end result can, literally, bring a timepiece to a halt. This fact was drilled home most poignantly for me when a client brought in their recently purchased Franck Muller wristwatch for service because it had suddenly stopped on them. When I checked under the hood to see what was amiss, I was surprised to encounter the following sight:
Corrosion had built up around one of the arms of the pallet fork, causing it to jam under the pallet bridge, as can be seen in the image below. There was no other corrosion evident anywhere else in the watch and the case itself proved water resistant when tested.
This degree of corrosion in such a concentrated area, in an otherwise perfectly functioning watch, is not something I had ever encountered before. The arc along which the corrosion formed, which can be seen in the smaller image below, suggests that a large drop of epilame was applied to the exit pallet and was left to dry under humid conditions without being subjected to a flow of warm air.
What is most unfortunate about this is that, in the case of the pallet fork particularly, it isn’t necessary for the steel to be subjected to epilame. The only active surfaces requiring lubrication are the ruby pallets themselves, which cannot corrode.
There are a number of different approaches to applying epilame to the pallet fork. The method we employ, which has proven more or less failsafe, is to use a small, tinted, dropper bottle to apply a sufficient amount of epilame directly to pallets. The dropper makes for easy and relatively precise application, while the bottle itself keeps the solution protected from light and premature evaporation. You can find these dropper bottles at most specialty health stores and scientific lab supply shops. Amazon also carries them for less than $2.