hey, sorry for commenting so late, wasn't well for some time..
this pouring or fluid art technique is getting quite common these days, and it's actually very fun. and like you said, one never knows what the final result would be, it makes it more interesting
so I do not use a brush for spreading the colours, instead move my canvas around and sometimes uses a blowing tube to give special effects.
thank you so much for your comments, really appreciate it, I was myself tired of using monochromes, thought of taking a break and doing something different, glad you liked it. <3
Love and a big hug