The brush really plays a crucial role in the work. There will not be a "random" brush, you need the same one for this technique and for you personally.
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Let's figure out what kind of brushes there are in general. We divide them into two types: synthetic and natural. It is important to have both for different parts of the work. Now I will tell you about each in more detaile.
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If we talk about natural pile, it is more often a squirrel or a goat. I really like sable brushes. Of course, they are more expensive and better than others, but they combine the necessary elasticity and softness. For beginners, I always advise to have only one natural large brushe. When the brush is small, it will be difficult for you to keep water in it and wash out the fragments you don't like. From my preferences, the firms da Vinci and Raphael are great.
Synthetic brushes have become more in demand and popular in our modern world, and that's why: now many companies make sufficiently high-quality synthetics that are ready to replace natural brushes by properties. Such brushes can cost less than natural pile, but perform almost the same functions. In addition, it is easier for beginners to work with them. Important! Do not buy synthetic brushes that are too cheap. Brushes are very important, because using the brush you can beautifully apply paint or completely ruin all the work. I prefer Escoda, Leonard, da Vinci.
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And most importantly, before buying a brush, check that the tip is sharp and the brush itself is elastic. Ideally, it should bounce off your fingers when you touch it. If the brush turns out to be too soft, it may mean that when it comes into contact with water, it will get wet and will have a blunt edge. If possible, test it in the store and feel how comfortable it is for you to work. Also remember: it is better to have one, but a good brush than hundreds, but cheap. Checked by me personally!