Thought I would return to this technique, which I tried in my first project without spectacular results. As usual, it's always the easy shots that are the hardest to bring off!
@suzanne234 Suzanne, there are much better shots than this I've seen on here. Basically you drop a small thing (piece of fruit, perhaps) into a container of carbonated water. Setting up the shot is relatively simply - making sure the focus point is right, fairly fast shutter speed, ample lighting (preferably that doesn't reflect off the container). Taking the shot can be tricky (I think I must have taken about 40 shots for the above). Then you hopefully have a selection to choose from for further processing. Sounds simple, doesn't it?
@caterina You could try bouncing the flash (if you have an angled flash head); failing that, try a white card placed in front of the flash to direct the light up (or to the side). In this shot, I used the spotlights on my overhead hob extractor unit (not sure what you would call that in Italy, probably the same thing!) which would have been adequate. Yes, I did use an external flash (a fairly affordable wired extension that I bought through Amazon) but I am pretty sure I could have made it all work without. Best of luck!