If you add the carbonate to twice the specified amount of water, you don't have twice the volume of solution. And consequently, you don't have exactly half-strength Part_B.Originally Posted byjuan

How much does this matter? As you say, if one is consistent, there is unlikely to be a problem. In fact, you might have found a slightly better formula than Sandy! At least for your chosen film. I don't know. I was just talking about the mixing concentration.