So, I imagine some people can afford to waste paint. The Hiltons, perhaps. Or a US senator. But, for most of us, painting is only slightly more cost-economic than a good heroin addiction, and wasting paint adds up quickly. As such, most artists have their own methods of conserving paint. I knew a lot of people who would use saran wrap to cover their paints and extend their use another day. Me, personally, I use a combination of two different approaches.
While I’m working on a piece, sometimes getting the color I want is a trial and effort deal, and it can lead to me making a rather sizable amount of paint for very little use. If I’m going to paint more that day, the first thing I’ll try and do is alter the left over paint into another color I can use. This can be done frequently, and it helps lead to related hues with a minimum of work, which helps make for a richer but still unified color palette. It also helps lead to my characteristically vibrant color choices, since I tend to mix colors strong to convert the original hue into a notably different one so I don’t waste the paint.
The next solution I have is one taught to me by Scott Anderson, and that’s to have at least one another canvas I’m working on at the same time. Then, at the end of the day, any paint left from the primary focus can be used on the secondary one, either modified as above, or frequently straight from the palette. (In the future, dedicated art historians will be able to tell in what order many of my paintings were done and which ones I did at the same time by the prevalence of colors carried over across works. Those historians will be far better at determining this than me, and will have far more time on their hands, I promise.)
Or, if you’re just getting a new one started, like I am here, it’s open season. Any paint left at the end of the day, no matter the color or purpose, gets scraped, brushed, or knifed off and onto the primed canvas. There, it can be worked with brushes, palette knives, or thinned down with OMS as this one was to create streaky washes. This helps build texture and background depth, which do nothing but good things for paintings, and since it’s going to get painted over anyway it doesn’t matter how you build it up, just so long as you do. Leftover paint is made for this.
For the point, here’s a detail of the primary canvas I’m working on. If you look, you can see a sort of lavender highlight in the left side of the shot, and there’s a brownish detail color used in the blue figure to the right. I ended up with way too much of both of those colors, and if you look back up to that new canvas, you can see how they got moved over there (with palette knives), and then I washed them down. But, I had very, very minimal paint left on my palette to waste to the cleaning cloth last night. And I’m getting a really nice looking surface for my next teacup piece at the same time. Win-win.