One of the odd jobs I did this weekend was to dye a litre of brake fluid blue.
On a racing car or a track car you change the brake fluid often. The job is either difficult or wasteful because it's pretty much impossible to tell whether you're bleeding out last year's fluid or the fresh stuff you just put in.
You used to be able to buy DOT 4 brake fluid that had been dyed blue to help with exactly this problem. You would alternate colours each year and be confident that you'd flushed out the whole system. However the Department of Transport standard for type 4 brake fluid specifies the colour as "straw", so the blue stuff doesn't comply with the standard and can't be sold as DOT 4. To be fair it would look to the MOT man a lot like you'd accidentally topped up the brake fluid with screen wash.
Some enterprising amateur chemists think that the dye is Methylene Blue. I've bought a gram of it and I'm trying it out. I think I've put about 50mg into a litre of brake fluid. It dissolved easily and it's now a clear and vibrant blue colour. I think a gram of the stuff would be enough to dye a large river.
Richard "That's Probably Why Walter White's Methamphetamine Turned Blue" B
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