Watercolor artists have varying opinions on how to produce white with watercolor. But perhaps "produce white" is misleading because actually, what most artist do is to preserve the white of the paper to achieve white in their work.
Most artist are from the school of thought that it's best to keep the white of the paper free from color while other artist will use mediums, like white ink or acrylic paint to incorporate white in their work.
I’m from the school of thought that you should do whatever works. After all, here are no watercolor laws that will be broken or watercolor police that will cite you if you use one method over the other.
3 Methods Outlined
1. Freehand/Paint Around
3. Paint/ Write Over
The freehand method requires a steady hand and some preparation. In my example below, I lightly traced out the design and after the watercolor completely dried, I went back and erased. If you use pencil, be careful not to paint over the pencil as it cannot be erased once painted over.
Although the freehand/paint around method may seem a little nerve-wracking, it's my favorite technique. I guess I'm somewhat of a control freak, because as you will see below some of the other methods aren't very good at keeping the white of the paper protected.
The resist method uses things to act as a barrier between the paper and watercolor. Some mediums or barriers work better than others. Below are examples of masking fluids, stickers, and wax.
Good for large areas. Not good for small details.
When using masking fluid it's best to use an old paintbrush that you wouldn't mind messing up as the fluid quickly becomes sticky and gummy and may ruin your brush.
Masking Fluid Pen
NOT good for large areas
Hard to peal off
I recommend using a masking fluid pen for very small details or for highlights.
I feel that my hello heart example was too much for the pen.
I LOVE using stickers as a barrier, especially the letters from Sticko! These stickers do a great job protecting the paper creating crisp clean edges. They also peel off super easy without damaging the paper.
* When purchasing letter stickers, make sure that the counters of the letters are cut out.
My heart sticker didn't do so great as you can see where watercolor leaked through.
As you can see, the wax didn't hold up too well. I used a plain ol' Crayola crayon. In my opinion wax would be perfect for paintings with a loose organic feel. For example, things found in nature like the veins of leaves, or feathers.
Another way to incorporate white is to write over the watercolor with ink or paint over it with acrylic paint.
In this example, I used the Uni-ball Signo white pen. They are awesome!! A white Sakura Gelly Roll pen would also work great.
Using white ink is super easy to use and have great coverage too.
Acrylic paint or even Gesso also works great at adding white over watercolor. I like how paint isn't as opaque and allows some of the pigment to show through.