Recently, a reader Tommy Olrich asked me this question in one of my videos on Youtube:
So i notice you don't take super duper care to keep your pans uncontaminated from other colors. won't the other color like seep into the pan and ruin the main color thats in there? i always get so paranoid mixing colors because i think I'm gonna ruin the premixed pans.
When it comes to watercolour pan boxes, there are two types. There are those watercolour that come with hardened pans or cakes. And there are those that you squeezed from tubes into the plastic pans. Those that are from tubes are usually easier to dissolve and reactivate with water. And because of that they are also easier to contaminate and more difficult to clean.
I paint mostly with watercolour pan boxes nowadays. My workflow starts with using the lightest colour first.
Yellow is the colour that's easiest to contaminate. That's why I use it first. Even a speck of blue in yellow will turn it green.
I usually put drops of water into the pans to soften them up. It makes it easier to dissolve them when I go in with the brush, and I can pick up a large amount of paint. Then I mix in the mixing area.
Colour contaminate usually occurs for me when I want to charge in additional colours into a wet wash. For example, if I have an Ultramarine and Burnt Sienna mix, and I want to charge in Permanent Alizarin Crimson (PAC), I would just dip my brush straight into the PAC without cleaning it first. So some of the paint from earlier mixture will contaminate the PAC. So the next time I use PAC, there will be some traces of Ultramarine and Burnt Sienna.
Generally speaking, colour contaminate is not a problem unless it's really bad, like you have a colour spilling over to other colour. A little contaminate adds character to your mixes. In real life, colours are not as vibrant compared to those paints in the pans. The pigments have to be extracted and purified from minerals. If you use colours straight from the pans without mixing, the result will look jarring.
So yeah, a little contamination is not a big problem. Just be careful when using brighter colours because they are easy to contaminate. The primary colours like red and blue are strong and even when slightly contaminated, they are still able to retain their original hue quite well.
Cleaning the contamination is something I dislike because you're wasting paint! It happens rarely for me, except for the time when my tube paint wasn't dry and spilled over to other colours. Thankfully, it was yellow that spilled over to the stronger red. If it was red on yellow, it would be a total disaster.
Here's my video response that talks about the same thing I've written above.
It's quite an interesting question, and the comments on the videos were also quite insightful because many shared their workflow.
One artist shared that he has two separate pans of the same colour, one for mixing and one for the clean colour.