I work for a bath bomb manufacturer and we are working on a recipe that needs to include 3-5ml of essential oil in each single bath bomb. The issue is that when I add that amount of essential oil into the mixture (before the bath bomb is pressed into shape), the mixture dries out too fast and basically turns into powder / hardens up (it dries out in like 60 seconds, which is too short of a time for me to press most of the bath bombs into shape). We sometimes make mix the ingredients into batches that are enough to make 45 bath bombs, which means that we add over 200ml of essential oil. We may try smaller batches, but this would need a lot more time and labor, which we're trying to avoid. The ingredients for the bath bombs are baking soda, citric acid, a pinch of salt (sometimes), water (very little) and some colorant. The goal is to get between 10-15 minutes of workability before the mixture dries so that I have enough time to press the entire mixture into shape. I know it's possible, but I just need a chemist to help me tweak the proportions or the formula.
Try mixing the essential oils with the salt or colorant and water before adding to the baking soda or citric acid. If that doesn't work, then you may need to tweak formulation. I am happy to chat by phone through the site if that helps.