What the carrier does
Pigment particles do the colouring; the carrier delivers them. Common carriers are purified water, glycerin (holds moisture, smooths flow, slows drying), isopropyl alcohol and/or witch hazel (disinfects, thins, speeds drying), and sometimes a little rosin or binder.
More glycerin means a thicker, slower, more forgiving pigment that stays wet in the cup. More alcohol means a runnier, faster-drying pigment that some artists find implants crisply but dries out and shifts shade as it evaporates mid-session.
Practical effects
Thick pigments are easier for beginners and good for shading; thin pigments can be better for fine detail but punish a slow hand. Artists often adjust consistency with a drop of approved thinning/mixing solution rather than water.
Hygiene and shelf life
Carriers with alcohol resist contamination better, but no open cup is sterile — decant only what you need, never double-dip an unclean needle into the main bottle, discard the cup after each client, and respect the printed expiry (typically a couple of years unopened, far less once opened).
