Matting is a "negative" technique, that is, you apply paint evenly, and it is by removing paint with a bristle brush that you achieve SHADING. For matting, you will need:
Special note: matte colors are blendable. While there is no reason to mix them in your palette, you may want to apply different matte colors on a project and blend them into each other a bit with your badger blender brush.
APPLYING MATTE, first step:
APPLYING MATTE, second step (see uniform matte with horizontal motions, and stippled matte with staccato vertical motions):
Wait until the paint is dry, then remove with hog bristle brushed that you will trim flush with small scissors. If you put a lot of gum arabic, it will be difficult to brush off, but feasible. If you didn't put enough, the dried paint will be completely removed by even the gentlest brushing, making it impossible to achieve shading.
Below is the matte before the "negative" painting by brushing paint off. I am using RP1139, Umber Brown Hancock's as I believe its warm yellowish cast will complement the hot colors in the butterfly nicely. It's a very useful tint.
First, remove all paint that lies outside the area you want to work on, and clean the dust off. Try to have many intensities of shading in your design, not just "matte on" and "matte off." It will be more attractive if you have areas that are 10%, 25%, 50%, 80% matte etc.
Mattes, depending on your chosen color, are generally fired at temperatures varying between 1180-1250F.
The badger blender/stippler brush
A British blender/stippler brush costs over $300 - but take comfort in the fact that it should last a lifetime. It is a specialty item. Badger hair is like no other. The hair spring apart, rather than lump together when wet. There is no substitute. If you can't afford this brush, or are waiting to become more sure of yourself before spending this amount of money, you might want to practice with a lesser brush and tolerate some streaking in your matte.
To take good care of your blender/stippler requires that you clean if after each matte application. Wet the tips only, and swing the water out with a hard wrist flick in the sink, like nurses used to do with old-fashioned thermometers. If you matte silver stain, you'll need a deeper cleaning. Use a bit of shampoo, foam the hair gently, and rinse generously. Flick out most of the water, and pat dry gently on a clean paper towel.