A tip I use when spreading diamond on a lap when charging to keep contamination to a minimum and also keeps your fingers clean. Wrap some saran wrap around the finger you use to spread the diamond. I tear off a small piece, double it, then wrap it around my finger tightly.
I often use Gearloose’s diamond sticks when charging so contamination at that point isn’t an issue. However I hold the stone itself while cutting, which will get diamond on your fingers. I often use nitrile gloves, and sometimes just finger cots ( the little single finger “condoms”) on my thumb and forefinger to the same end as the plastic wrap mentioned above.