I have evaluated about 80 different soap bases and about 180 soaps. I have devised a method of lathering which works with nearly all of them with the exception of soft creams and triple milled soaps. They require different techniques. Here is my method for most soaps.
1. Place the shave brush into a container of warm water so the bristles are covered but not the base of the knot.
2. Measure 1 Tablespoon (15 ml) of hot water and add it to the tub of soap. Swirl it around gently in the tub until you get a milky liquid. Depending upon the hardness of the soap, this can take anywhere between 10-30 seconds. With soft creams, I skip this step. For triple-milled pucks that have dried completely, this could take quite a while.
3. Dump the milky liquid into a lather bowl.
4. Remove the brush from the water. Squeeze out excess water and then shake the brush vigorously four time leaving the brush damp, but not wet.
5. Load the brush directly from the tub or tin swirling at a rate of two revolutions per second until approximately 1.5 grams of soap are loaded. Loading time will depend on the type of brush, the pressure used to load, the softness of the soap, etc. Soft soaps may load in as little as 5 seconds. Firm soaps might take 30 seconds load time. Most of my soaps will load in 10-20 seconds. Some triple milled soaps might take a minute. With creams, I will scoop out an almond size blob of cream directly into the lather bowl.
6. The lather bowl I use is the mortar bowl from a mortar and pestle set. The bottom is rough making an ideal surface against which the brush can work for generating shear for producing a lather quickly. The first few swirls have to be gentle to avoid splashing the bloom water out of the bowl, but once the water and soap have mixed I agitate vigorously until all large air bubbles have been eliminated. For the best soaps in my den, I can produce a great lather in about 30 seconds. Some lesser soaps can take up to 1 minute before large air bubbles are gone. . Soaps that are difficult to lather like Williams Mug Soap might take a minimum of two minutes of lathering with even longer times being beneficial. I do not have the patience to lather difficult soaps.
7. I then apply the lather to my face. If the lather does not apply smoothly, I will add additional water about 1 ml ( 20 drops) at a time until the lather is smooth and slick.
8. To check for proper hydration of the lather, I fill my sink with water and leave a slight trickle of water so the surface water goes out the overflow. As I shave with either a straight razor or safety razor, I dip the razor gently into the sink water. If the lather sticks to the blade, the lather is too dry and I add water. If the lather dissipates immediately, the lather is too wet and I add a little more soap. Normally, the lather will be about right and the lather will release quickly from the razor and float largely intact to the surface. There is a range of hydration that will do this, so you can make the lather slightly drier or wetter depending upon your preference. Generally, a drier lather will have more cushion and a wetter lather will be slicker, so adjust the level of hydration to provide the balance of cushion and slickness that works best for you.