How many times have you walked away from a canvas thinking your highlights are just right, your value shifts between light and shadow are just right. And a couple of minutes later they are gone! I know I have!
This is because the acrylic medium that is mixed with the pigment to make acrylic paints is a little opaque when wet - and then drys clear.
It's hard to pin this down because it isn't the same for all colors, so I thought I would try an experiment.
I used gessoed canvas and these paint colors in Golden regular heavy body paints:
Napthol Red Light
Hansa Yellow Medium
I made rectangles of each color, using a double layer so I would be sure to cover the white canvas.
I added white to these and made more rectangles of paint in different values of the same color.
After letting them all dry, I used the exact same mix and brushed the wet paint over the dry and took a photo immediately.
The dry paint is on the left, the wet paint is on the right.
So this is what I saw:
First with Napthal Red Light:
The middle one with white added also shows very little shift (the wet stroke is always on the right)
The last sample, with quite a bit of white added shows a significant shift in value from dry to wet. It's pretty obviously lighter on the right!
Next with an Orange made by mixing Napthol Red Light and Hansa Yellow Medium
Another interesting thing to note on this sample. My mixture of red and yellow to make this orange looked very similar to the red in the pure form. But notice how different the color looks when you add white?
Next is Hansa Yellow Medium
Again, no visible shift in the pure tube color. Even in the lightest version, the shift is not that big. Interesting! Hansa yellow is not a strong color. In mixes you have to add proportionally more of it to get it to show up.
Next is Green made by mixing Ultramarine Blue and Hansa Yellow Medium
Again, a fairly transparent color from the tube, so even after 2 coats of paint on the left, the wet paint on the right is still darker because it is covering more of the canvas. Our pattern seems to be pretty consistent! No wonder my sky always looks too dark!!
Lastly, a Purple made from Ultramarine Blue and Napthol Red Light
So, this was a great experiment for me! I say all the time in my classes "Remember, acrylic paints dry darker!" And now I can show you just how much!
- So the pure tube colors don't shift much. In fact the transparent ones may look lighter - just because there is more of the canvas showing through and a double layer of the same paint will cover more.
- The more Titanium white you add, the greater the value shift from wet to dry!
- When you mix those very light colors, like for sky and highlight, don't be afraid to go very very light! What looks almost white wet will dry obviously darker!