To my mind, the only method that is feasible for "ghetto scale" attempts at even mild purification or isolation of Meth vs cuts are fractional freezing aka fractional melt crystallization (there are about 10 different terms that describe vaguely the same process)
The simplest design is a tube wherein a mixture is carefully heated to melting point repetitively at a slope, allowing the mixture to transit the tube.
process optimization typically involves a heating program that starts out high, at or above the MP of the higher MP compound, and progressively decreasing to favor the lower MP compound, along with considerations for microscopic (diffusion) and macroscopic (melt flow rate) variables. For example heating element might be cycled first in a logarithmic fashion (slowly turned off, allowing the melt to flow) and progressively transition to a step function (full on to full off)
This might sound infeasible to "ghetto scale" processes but remember:
its 2021. There is an entire industry supplying the people who vape with the equipment necessary to create custom nichrome heating elements at home.
additionally, welding quality inert gas supplies are relatively cheap and available used in plenty of places.
Most population centers, certainly in North America, have borosilicate glass suppliers relatively close by making it possible to obtain glass tubing easily and with cash purchases.
The nice thing about this method is that it uses no solvents or overly policed equipment. For example you dont even have to request a single packet from a single server dedicated to selling "lab equipment"
also, if properly setup with the right heating and inert gas, there is low risk of loss of material for people who are worried about economic risks or unsure about their technique and who may want to preserve even the cutting agent if they feel like its not working out.
