I got coerced into this. A hot water cylinder had a small leak damaging the ceiling below. I cut it all back, but in doing so uncovered a section of wall I had scumbled and stencilled 20 plus years ago. The wife went 'ooh I like, do it again'. In fairness I enjoy doing that stuff. Over the years I have marbled, colour washed , ragged, stippled, dragged on everything from ceilings ,walls, to furniture. Had thought I might be done with all that ,but apparently not. Thought just buying a scumble might save me making my own although it's not that hard. Bit of boiled linseed oil, add white spirit and the artists oil colour of choice and away you go. I will say this stuff is mega durable although the oil content can lead to colour change over the years.
Well, now you know more about scumble than you wanted , or needed to.