I had a few people asking me how I did the art for the alchemy cards set, these are the screenshots from unstable gas.
Step 1, find a picture of a bottle online, any bottle would do, if you have in your mind the final version it is even easier to find the right one:
Step 2, distort (warp and liquify) the bottle until it has the shape you had in mind
Step 3, add the bottle as multiple layers on top of a background, lights on the top layer, shadows on the bottom one, give some transparency to each layers (bottles and liquids are transparent) sprinkle with effects here and there: done.