I bought these synthetic watercolor brushes a few months ago at Jerry’s Artarama. They are made by Creative Mark. The black and tan ones are Beste Fountain and come in a 4 pack with a demo DVD. The all black one is the Beste Dagger Stripper 1/2. Very versatile and durable brushes. From fat washes to this lines. I always keep them in my arsenal. Go buy a pack and you will like them. About 35 bucks for the pack I think.
Pure sable brushes are so expensive. I have one that I use occasionally, but pretty much use the synthetics. I have two flat synthetics I have had for 29 years and I still use them. Me being careful with brushes helps.
Tip of the day. Never let anyone other than me use your brushes or dip pens. They will always screw them up. I won’t ’cause I’m careful! 😉