"One of the major changes I've made in the last year is switching from waxing my thread with beeswax, to using coad.
Coad (also called code, shoemakers wax, sticky wax, black wax and a dozen other names) is a mix of beeswax and one or more pine resin materials. Coad acts as both a lubricant and a glue; as the thread is pulled friction melts the coad, allowing the thread to glide through the stitching holes, once the thread is pulled tight, the coad sets up acting as an adhesive.
There are dozens, if not hundreds, of different coad recipes. Many of the traditional recipes are designed around producing a black wax and utilize a black pine pitch. This pitch has become difficult to source over the last 50 or so years (even the shoemakers at Williamsburg have trouble getting it), while some of the newer black recipes substitute tar for the pitch.
Most recipes have done away with the black compounds resulting in a "blond" wax. With the widespread availability of colored thread there's really no reason to deal with tar fumes, or in trying to source a material that only two companies in the world produce.
The blond recipes work as well as the black recipes and are much cheaper and safer to produce. I use two different recipes depending on the time of year. I don't have central heat and air in my house, so the temperature tends to run a bit warm in the summer and a bit cool in the winter, and I adjust my coad to suit these temperature changes.
My coad recipe(s) consist of two materials, beeswax and rosin (I use rodeo rosin, $10/pound on eBay, a pound should last a decade or more).
The measurements are by weight, don't go overboard, close enough is good enough. The smaller the components the faster the melt. I can generally crank out a ball in 15 minutes including weighing the material.
Winter recipe: 1 part rosin, 2 parts beeswax.
Summer recipe: 1 part rosin, 1 part beeswax.
You will also need a bucket of cold water. Melt the rosin first, it has a higher melt point and takes longer to liquify. I use direct heat, I've had poor results attempting to melt the rosin in a double boiler. If the rosin starts bubbling lower the heat and pull the container off until it cools a bit.
Once the components are liquid and thoroughly mixed, pour them directly into the water. This flash cools the mix, lowering the temp to a point that it can be handled. Wad the mass up in the water, this gives a chance to check temperature without risking burns. You want it warm, but not too hot to handle.
Pull it from the water and start taffy pulling. It'll feel a bit gritty at first and will probably just tear apart for the first 30 seconds or so. Just keep at it - it'll start to smooth and the stretches will get longer. You're probably not going to get a 100% amalgamated mass - you'll probably see little flecks of rosin throughout. That's fine, just try to get them as small as possible and thoroughly mixed through the mass.
Once it gets difficult to pull start squishing it a bit and then ball it and set it on a piece of plastic or wax paper. Let it set and cool overnight.
To use, run your thread across the surface of the ball and then either pull the thread through your hand, or a piece of cloth a few times to heat the coad and disburse it a bit better, and start sewing.
Since switching to coad I've had zero issues with knots untying (no more knot burning) or back stitches unthreading.
If you knot while stitching (I do on some projects) the coad really locks the stitch in place. The few items I've had to dismantle since switching to coad have required the parts to be fully cut apart (along the stitch line) and pliers were required to remove the remaining thread."