I thought it might be nice to take you through a step-by-step of how I paint my goldfish. I did it once with koi, but I think this one is a little more thorough.
I start with my sketch. Sorry, I know this is hard to see. But there are three fish: a main fish, slightly off center, a secondary fish to the left, and a third fish in back. I take some artists tape and cut out shapes for the eyes and put them on the paper. This does two things - it keeps the eyes clean for a different approach to painting them, and it helps me see where the fish are when I am lifting.
I put the first wash of background color on - right over the fish. I used Cerelean Blue, Prussian Blue and Sap Green. I have already started to lift out the first fish with a damp squirrel hair brush. This is done while the paint is still wet. See the eyes on the other fish?
Now that I can see the fish clearly and the back wash has settled, I do another wash below the fish - pumping up the Prussian Blue where I want a stronger contrast.
I do the same thing on the top part. (I also sprinkle some drops of water to give the illusion of air bubbles.)
I underpaint the fish with a combination of blues, grays and Burnt Sienna. One of the reasons I am using Burnt Sienna is because the frame this will go in is that color - so it will look like it fits. I mainly paint on the bottom, where the natural shadows would be.
After the underpainting is completely dry - I can lay the yellows, oranges and reds in on the top fish. Before I paint, though, I do a loose water pattern on the fish (NOT a full wash). Then when I put the color on - some will bleed and some will lay flat giving me wet and dry areas of paint which make it more interesting and true to life.
Now that I have stronger colors on the front fish, I can see the background fish is looking pretty pale. I have to intensify those shadows.
Now I can put the colors down on this one too. I went for a fully colored fish, just to be different. If they are all the same - it can be a little boring.
Now comes the time for finishing up. I rework anything I think needs to be darker and show more contrast. I lift some scale highlights out toward the top and add some darker scales in toward the bottom. I also remove the tape covering the eyes and paint those in using light blue, yellow ochre and black for the pupils.
When I finally think it looks good - that nothing I can add will make it better - I put my seal in the bottom corner and sign it.