When I first set out to make FWFL, Ivory soap was a detergent and did not include sodium stearate. I found one version of Ivory soap that was a throw-back, of sorts, the label said it was the old style with sodium stearate. Then I read the label, and it had two optional sets of ingredients - one being soap and the other being detergent. I found that unreliable.
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So I bought lab grade sodium stearate from Amazon. I use 10 grains of powdered sodium stearate in a normal batch of FWFL, which may be more or less than Felix’s original intent. The pain is that powdered sodium stearate has to get very, very hot to melt and doesn’t dissolve well in mineral oil.
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I have modified FWFL for a higher melting temperature, which includes microcrystalline wax (180F melting temperature, bought on Amazon) and I also use bees wax soap. I add paraffin wax so the final product is not so sticky. When I made my last batch of lube, step 1 was to melt the microcrystalline wax and paraffin wax (3 parts MW & 4 parts PW) and then add the soaps. Low and behold, I found the soaps dissolving into the wax at a surprisingly low temperature (200-ish degrees F). So that solves the high melting temperature issue noted above.
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If you do not want the added wax to modify your lube performance, you should be able to dissolve sodium stearate in microcrystalline wax alone, and you could probably get away with very little MW. At that point, the MW would may be meaningless to the final product.