I am currently building a 1800 piece set in 'Light Bluish Gray'. Essentially using a OEM set but 'gray'y'fie' it.
Anyway - I already had most of the pieces I need (after weeks of hunting - and actually still waiting for some) but there are SOME pieces, in fact, impressively only about 2 in 1800 , that simply aren't made in LBG.
So there were a few options - dark gray - which was one of the options - or paint it.
I have been crawling through articles in order to find the color code - it's unreal the time I spent.
So then the idea - I knew about the fact that acetone melts lego and I found a 2013 post about melting lego for the sake of paint (happy to post link if allowed).
Now it took me quite a few attempts to get the correct consistency.
I still need to play with some sanding - but as I say - pretty happy ..
So here the 'slush' - I noticed that not all pieces are able to melt in acetone ... the perfect brick I found are the 2x4 - they melt in minutes. Then just add acetone to get as thin as needed. I used to stir them a lot but bubbles are pretty persistent ... With resin you can use a heat gun - but with something soaked in a flammable liquid - probably not a good idea - so I just stirred slowly.
Then I used it as a paint - potentially workable - but I THINK you'd need to find a good brush (and lots of sandpaper)
Then I made it really thin with more acetone ... then I grabbed a piece that was send in a wrong color (thanks) and dipped it ... OMG
So for me I need #4742
in LBG - no chance ... so I bought a dozen of Dark Gray ones for testing .. half a dozen later I found the perfect consistency
I am giggling like a little girl .. works perfectly ..
The next step is to sand them down a bit - I got grits from 400 to 7000 so probably start around 800 / 1000 ish and see how it goes.
I am not sure how durable they are obviously .. All I can say is that I destroyed a few spoons where I can't get the stuff off lol ... but this is for a gray'y'fied UCS set so I am not worried about playability .. But after 6hrs of drying I can see SOME shiny parts still .. but I can touch / use them without destroying - but I think it is better to dry over night and then give a them a bit of a sandpaper treatment.
I have a few technic pieces that are an odd shape - but they won't show in the set (they are dark gray as opposed to light gray) so I am not worried (or damn, maybe I should order more pieces and give it a shot).
Anyway .. so yea - don't kill me as a purist - I got virtually killed on another forum for even thinking about melting bricks - but personally I don't care if it works for me ... :) :)
Anyway - with a nice sealed jam jar the stuff lasts .. seemingly forever .. and all it takes is a few drops of acetone to not just clean your tools but to get it a bit runny again when it starts to dry up.