Black hole is the only element in the "specials" section that can be made via reactions. If you mix pressurized invs and warp, you get black hole (as demonstrated in the black hole machine.) Oddly, this ONLY works when invs is pressurized.
Well, black hole is still the only "special" element that can be made by means other than the brush, the console, or CONV. White hole, for example; can only be made by these 3 things. By contrast, there are 4 ways to make black hole. And mixing pressurized invs and warp is the 4th way.