How to make a double-boiler for waxing the pickups

What is a double boiler and why do I need to use one?  

A double boiler is a pot within a pot. The outer pot contains water which safely transfers heat to the inner pot without allowing hotspots that could exceed the burning point of the wax and start a fire.

Never melt wax in a single pot directly over a heat source!  You can easily make a double boiler from a pot and a large tin can – one- or three-pound coffee cans and "family-size" soup cans work well depending on how much wax you need to melt or, as in the case of potting guitar pickups, how large an object you need to immerse in the melted wax.

Waxing the pickups to reduce feedback

Be safe! 

The inner container of a double boiler must be well isolated from the outer container. This is the entire point of a double boiler – isolating the flammable wax from potential hot spots caused by direct application of heat. An improperly constructed double boiler like the one on the right below might provide some protection but is not really safe because the metal-to-metal contact at the bottom of the containers can pass hotspots even with the surrounding water. And if you are interrupted and the water boils away you'll probably get an opportunity to check the response time of your local fire department.

Never use an open flame (i.e. gas stove) to heat your double boiler.  Melted wax splashes and drips easily.  If splashed wax is also set alight by open flames you've basically created a poor-man's napalm!  If you have a gas stove you can purchase an electric hotplate for a few dollars at a second hand store.  Always wear safety goggles.  Gloves and an apron are highly recommended.

You can make a safe double boiler out of things you have around the house

At the worst, you may have to spend a few dollars for a large aluminum cooking pot and maybe a hotplate.  The outer container is a large cooking pot.  A cheap aluminum one is fine.  I used a glass one in the illustrations below just so you could see through to the inner pot.  The inner container is a tin can of the appropriate size with two pairs of holes punched in the side up near the rim. Always make sure that there is at least about 1" of space separating the inner and outer containers all the way around, including the bottoms.

Double boiler model 1

The first model uses rigid rods passed through the holes in the sides of the inner container.  The rods rest directly on the rim of the outer container.  Make the rods long enough that there is enough overhang to keep the rods from falling into the outer container even if the inner container is moved all the way to one side.  The rods can be of any rigid material that can withstand heat and steam.  Hardwood dowels, very heavy music (piano) wire, or metal tubing are all good candidates for these rods.

Double boiler model 2

The second model uses rigid rods like the first model above, but those rods are above the inner container and short loops of picture hanging wire are used to tie the inner container to the rods.  The inner container should be touching, or almost touching, the rods.

Double boiler model 3

The third model uses a long loop of picture hanging wire.  The wire runs through the holes in the inner container and is then looped over the handles of the outer container.  Make sure that handles are straight enough that the loops won't vibrate off and drop the inner container.  Remember that you have to leave enough slack to put the loops over the handles, and that slack will let the inner container ride low in the outer container.  Note that the wire is much thinner than depicted here – I rendered this using thick wire to ensure that it showed up well.

Using the double boiler

Whichever model of double boiler you use keep in mind that you do not want the inner container to float on the water in the outer container.  The level of wax inside the inner container needs to be kept significantly higher than the waterline on the outside of the inner container.  If you use too much water and allow the inner container to float it will be unstable, tipping from side to side, and the rods or wire loop might come loose.  The water level must be high enough, however, to partially immerse the inner container.  During a long session you might have to replenish the water from time to time.  The larger the outer container is in relation to the inner container the less frequently you will have to replenish the water.

Some people construct a much simpler double boiler using relatively narrow containers and no supports.  The inner container is underfilled with wax, so that it floats on the water in the outer container.  The relatively narrow clearance at the sides keeps the inner container from tilting enough to spill as it bobs around loose on the water.  Many people have probably used such boilers successfully but we cannot recommend this type of double boiler because of the fire hazard if you become distracted and enough water boils away to allow the inner container to rest on the bottom of the outer container.

Cleanup is easy with the double boilers illustrated here.  Just let the wax cool in the inner container, cover with foil (or the original plastic lid if you've used a coffee can), and store.  If you used someone's favorite cooking pot for the outer container, and dribbled wax into it, you'll need to clean it and that is most easily done while the pot is still quite warm.  If you're using canning wax, it's not toxic and has no noticeable flavor so you needn't worry about poisoning the family if a small amount of residue eludes your cleaning efforts.