Commercial watercolor paints usually come in two basic forms. Watercolor tubes are made of metal and filled with the bottom end open, with the tube already sealed and capped. Watercolor paint in tubes are soft like toothpaste and are easily soluble with water.
Watercolor pans are are made of a plastic or metal container. The paint is chalky and caked. Water must be mixed in with the paints to become soluble enough to use. However watercolor paint is purchased, protecting and storing watercolors will protect the quality of the paint and provided extended use.
Wipe paint clean. Prevent caking and crumbing around the edges of the tube or pan. Use a damp washcloth and wipe edges of wet paint until clean. Avoid getting pigment mixed together when wiping.
Soak dried paint with hot water. For tube paint that has been dried in and around the caps, soak off paint with hot water. Dry thoroughly before replacing cap on tube. Wet a paintbrush or washcloth with hot water to rinse away dried and crumbling paint around paint pans.
Replace caps on tube paint and screw tightly. For paint pans that do not have a replaceable cover, wrap plastic wrap around the container. Allow paint in paint pans to air dry for an hour or two to avoid mold buildup when covered. Keep watercolor paints in a cool, dry place. Never leave paints in a hot and humid area, as this can produce mold and separate the pigment from the binders and other fillers.
If watercolor tubes have not been used for a length of time, the pigment may separate from the rest of the binder. This looks like a oily substance separated from the pigment when squeezed from the tube. Replace cap and seal tightly and gently mix paint within the tube by pushing contents up and down paint tube.
Put plastic wrap around paint tubes that have cracked and expose paint. Fasten with a rubber band.
Avoid leaving paints uncovered for long periods of time. Dust, dirt and hair can build up and destroy the quality of the paint.