Chemically pure ethanol can be quite expensive due to increased tax, unless it is used for laboratory purposes. Denaturated alcohol (usually a mixture of ethanol and methanol) has been made undrinkable and therefore a lot cheaper. It can be used for pyro purposes. Some types of denaturated alcohol exist with other chemicals mixed in besides methanol to make it undrinkable and recognisable as such (colorants etc). I have no idea what these extra additives are and whether they can cause problems in compositions. I have been using 'spiritus' (a well known type of denaturated alcohol in the Netherlands) for several years without problems.