'Best for traditional slip joints' basically comes down to compound selection, used on most any relatively smooth & firmly-backed substrate that'll hold the compound (leather/paper/wood/fabric). As mentioned, black & green work well on steels used in most of these knives, such as 1095, Case CV, 420HC, 440A/C and their foreign equivalents, etc. White (aluminum oxide) also works well. I especially like green compound to put finishing touches on these steels, when used on leather.
David