If you add water the batch becomes clumped and crumbly as it dries
Oils or butters work best, without any other fluid - oils don't react with the mix, they don't evaporate quickly and they add moisturising properties.
You can use liquid oils with polysorbate - this never really worked too well for me, but I think most do.
Or you can use butters (any combo) with around 1% E wax (don't go too high or you won't have enough time to work with it).
If you add too much oil or butter you bombs will never set, too little and they will crumble.
I go more by feel than by measure, but usually 3 cups of powder to 2 - 3 tablespoons of oil/butter.
balls are REALLY hard to do, and your recipe needs to be 100% spot on, or they just don't work. I have just mastered them, but used muffin trays for ages, these are pretty fool proof, and give you a feel for the recipe, without a disaterous result.
Heres a pic of my lates that I made for a market - the ones with the hearts are made with muffin trays - and the balls - these are rock hard the next day
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Another tip is to sift the batch through a sieve WITH the oils, it ensures even distribution and saves heaps of time
Oh and Don't use 'Crackling Candy' (Pic back and far left) it reacted and left the uggliest looking spit globs on the top :?
Hope this helps, they are really fun to do once you get the hang of it