I decided that I'd craze the finish on the body - to give a lightly aged look, but still keep it looking shiny for now. (The bass will get any knocks and wear from gigging and playing over the coming years).
Anyhow, when I've cracked the lacquer in the past, it's been on guitar bodies - which I've just stuck in my freezer overnight. The size of a bass body doesn't fit into the compartments of my home freezer, so I had to think of another method of crazing the lacquer.
By chance, I'd met a plumber who was talking about freeing stuck pipe connections. He said, "when that happens, you just spray one part with Crack It spray. That instantly freezes the part and breaks the stuck connection". It turns out that this plumbers aerosol reduces the surface to minus 45 degrees.
I got a can myself from a local Toolstation. All you have to do is get the lacquer warm, then simply spray the aerosol on the surface. You can sometimes hear the lacquer crack. Anyhow, the end result is a nice crazed lacquer. As the plumbers spray has an oil in it, you need to clean the surface afterwards using a rubbing compound (I used Mer Car Polish). I've heard that some folk use aerosols of compressed air to reduce the temp. I might try that on my next build?
Here are some pics of some of the crazing (after crazing the lacquer, I wiped the body surface with water based Dark Oak stain to emulate years old grime in the cracks).