I made them a long while ago for my kiddies but can't remember where I placed my recipe so i went searching for another one online.
And i'm going to make more up in the next day or two using this recipe.
1 cup baking soda,
1/2 citric acid
1/2 cornstarch
1/3 cup epsom salt
2 1/2 tbs sunflower oil
2 1/4 tsp water or witch hazel
1/2 - 2 tsp Fragrance
1/4 tsp Borax
I didn't save the exact link (but they didn't post any picts anyways, LOL but I did copy and paste the directions and saved them.
Dry Ingredients:
1 cup baking soda
1/2 cup citric acid*
1/2 cup corn starch
Sieve dry ingredients until you get a nice smooth blend. (Optional: add 1/3 cup epsom salts or coarse sea salt after sieving. This is recommended if making bombs in a more humid area.)
Wet Ingredients:
2 1/2 Tbsp sunflower or other light oil (I use sweet almond oil, available at drug or health food stores)
3/4 Tbsp water (can substitute flower water, such as rosewater, or a combination of rosewater and glycerin)
1/2 to 2 teaspoons essential oils or fragrance oils (depends on strength of the oils)
1/4 tsp Vitamin E oil (optional, but recommended - an antioxidant which preserves the oils somewhat)
1/4 teaspoon borax (an emulsifier)
vegetable or other natural colourant (optional - a few drops of food colouring works well)
Combine all the wet ingredients and borax in a jar. Cover tightly and shake vigorously. Drizzle slowly onto the dry ingredients and blend thoroughly. It should not fizz while you are drizzling and mixing. If it does, slow down!
Pack tightly into moulds and slide out. They should release easily. Allow to dry at least overnight.
Mixing:
This mixture is very dry and crumbly and has to be packed in the moulds quite firmly to keep shape. If you add any other ingredients (such as herbs, epsom salts or dried flowers) you may need to add a bit more almond oil but try not to, because the mixture has to be quite dry. Too much oil makes the bombs soggy and makes a mess of your tub. I mix the liquids into the dry ingredients with my hands. That way I can feel if I need to add more oil. The mixture should just start to hold together when pressed in your hand, like slightly moist fine sand. Make sure it is well mixed.
Adding epsom salts adds a bit of shine to the bomb and also seems to make the fizzing action more vigorous. It also seems to shorten the drying time required. If you want to add coarse sea salts, I recommend breaking it up a bit with a mortar and pestle or in a blender. The grains should be about the same size as those of epsom salts.
Shaping:
This recipe makes about 4-60 mm round bombs. I use the clear plastic two-part Christmas ornament balls; you can also get an 80 mm ball (these incidentally are the same sizes as the Lush bombs). I find the 60 mm bombs are all you need for a nice bath, and I have a deep claw-foot tub. I have never needed to oil the moulds beforehand when using these plastic moulds as long as they are clean and dry.
I pack each side of the mould quickly, then throw some loose mixture on top and squish the halves together. (the mould needn't fit together completely; in fact it shouldn't, because then it is harder to get them apart). Don't twist the two halves, just push them straight together and smooth off any excess around the crease with your fingers. You can unmould them after a very few minutes onto a baking sheet.
Unmould one side at a time, taking the top half of the mould off first (you may need to tap the top gently once or twice), then turn the ball over and remove the other side. Avoid the temptation to *twist* the top of the mould, as this can easily split the bomb. If the bomb splits or crumbles, empty out the mould completely, crumble the mixture and start again. If the bombs crumble and won't keep shape, add a tiny bit more oil (1/4 tsp or less). If you have leftover mix you can either gather it in a jar or plastic spice bag, or put it in a smaller mould (I use half of a Christmas heart mould). The mixture shows detail very well; other people I have heard of people making smaller bombs by pressing them into candy moulds.
Sometimes the bombs crack a little around the seam after a day or so; just gently rub the crack with your (dry) fingers to smooth it. If you have a bomb split after drying you can still use it at home, use it as a demonstration, or crumble it up and use it as fizzing bath powder.
* Citric acid is sometimes available in drug stores but it's not cheap. If you think you might like to make a few, or if you have a friend who might want to try too, I suggest ordering a kilo or 5 kg pail from a reputable soapmaking supply house. Do not substitute ascorbic acid (vitamin C) as this makes the bombs discolour.
In regards to drying time, I let all of mine dry two or three days. I have heard it suggested that one could speed up this process by baking the bombs for two to three hours at very low heat (no higher than 200 degrees F), but I haven't found this necessary myself. I imagine this would make the whole house smell of them for days, which may not be your preference! However if you live in a humid location, you may need to try this.
Packing:
They look nice packed in cello bags or you could use spice bags such as are used at the bulk store. Tie with a pretty ribbon or nestle three in a small wicker basket for a nice gift.