Here's what you want to look for in a new brush, but as with many things there aren't any right or wrong answers. The brush you buy should depend on the situation. Fine brushes are great for detail, but a larger brush is best for terrain and basing. Art stores will provide the best selection, but avoid buying long handled brushes. Don't spend $20 on a brush intended to be used for spreading glue, go to a dollar store instead. Certain techniques are going to destroy brushes (dry-brushing, spreading glue, etc) so never throw out old brushes; they'll serve a purpose eventually.
The basics brushes you'll want are these:
- Fine detail brush (5/0)
- Medium detail brush (000 and/or 0 or 1)
- Cheap dollar store pack
Some brushes will explode, puff out or weaken.
Sometimes 1 or 2 hairs might get away from the brush. This can be fine if they only run away when you're not using the brush. If they still pop out while you're painting, you can carefully snip and continue using the brush.
Personally, I prefer synthetic brushes. Not only are they a lot cheaper than real hair, but I've spent a lot of money on some expensive real hair brushes only to constantly come back to synthetic for quality reasons.
When it comes down to it, I find they just hold their shape for much longer than other brushes. I don't know why - maybe it's humidity or the paint, but I use all my brushes the same, and synthetic just lasts longer. (Other people might have personal issues using brushes made from martens, squirrels, hogs, camels, ox, ponies and goats.) Synthetic brushes come in various colours of bristle, though the ones I use are white.
I mostly use H.J. brushes, with White Taklon (a synthetic) bristles, size 970 Round
I've started using a Princeton Spotter 20/0 for super fine detail though.
There are other types of brushes out there and high quality real hair brushes are supposed to be better than even the synthetic. (But at less than $3 for a synthetic brush, I can probably replace it as I need to)
Tip Size and Shape
There is a general measurement for the size of a brush. It starts at 00000 or 5/0 then 0000 and so on to 0, 1, 2, 3, and up. The higher the number, the larger the tip, the more 0's, the smaller. Unfortunately this is used more as a guideline and sizes may be slightly different from one manufacturer to another.
When you're buying a brush, inspect every tip. You don't want to buy one that's already lost it's shape. Also, check the size written on the brush - don't trust they've been put back in the right place as other people are browsing.
The sizes I usually work with are:
00000 or 5/0, 000, 1 and 3.
You can also get brushes with varying shapes of tips. Some square or rectangle, others that taper so that a square also has a sharper corner for mixing between coating and detail to get into recesses.
Painting and Detail Work
I prefer to use a 000 to apply first coats of paint and washes to larger areas, depending on how tight the detail is. A 1, 3 or a square tipped works better on larger creatures and vehicles. Use your fine brush to avoid colouring out of the lines, but not to fill in the larger areas.
When it's time to start applying detailed shadows and highlights, or you're working on areas that get really tiny, I switch to my 5/0. Even if you're working on large things, a detail brush is good at this point to avoid a streaking effect, and will let you blend your shades/highlights better.
(looking specifically at brushes - techniques will be in a later post)
Depending on the area you're dry brushing, you can use different sizes and shapes of brush. These techniques are very abusive to a bristles, so don't use a good one.
You can usually use the same size of brush to dry brush as you would have to base/wash. (Back to those 000, 1 or 3 sizes) If you're not working on a fine area, a wider square brush is nice because you'll not only cover a larger area, but can overlap your brushing to prevent visible streaks.
Since the bristles on a dry brush tend to explode, finer areas can get tricky as you don't want to paint outside the lines. You may prefer to manually paint highlights, be more controlled and/or use a 5/0 brush.
When doing controlled soft highlighting of areas rather than quick abusive brushing, finer thin or wide/square brushes become preferred - again, you don't want to colour out of the lines.
When working on terrain, a large square or fan brush is excellent to quickly highlight a bigger area - and again, overlapping prevents visible streaks.
Glue / Chemicals / etc
You want to use cheap brushes anytime you're working with something that will ruin a brush. Take a trip to a dollar store and buy two packs of cheap brushes - the large, wider ones and some thinner ones. I find it best to keep your "good" brushes and "other" brushes separate so you don't cause any unnecessary wear to your good ones.
Usually, you'll be spreading glue for flock and other basing techniques. Other times, you might be spreading paint thinner or a paint / chemical that doesn't clean in water so well, might leave junk behind in the bristles or even eat at the glue that holds the bristles in place.
This is somewhat out of scope, but keep in mind that you're not limited to painting with brushes. Foam and sponges can create some nice speckle effects if you get most of the paint off them. (like when dry brushing) Picks and sculpting tools are better when spreading paint in water effects or when painting things you want to be streaked. (blood, ooze, etc) Sometimes you'll even want to smudge something with your fingers.