Three bottles sit on the shelf at roughly the same size, all holding something clear and watery. One says essence. One says serum. One says ampoule. The ampoule costs the most, so you pick that one up first and assume the word has been earned. Almost everyone reads those three as a strength ladder with essence at the bottom and ampoule at the top. It is a fair guess. Ampoules do tend to come in smaller bottles at higher prices, and smaller plus pricier usually means more of something per drop. The guess falls apart as...