most brands work well, but all have a use by date, and you can tell by the colour of the hardener, it goes a darker colour. I use the cheap medicine cups for mixing my epoxies, that way you can get a fairly accurate mix. Again avoid to much hardener, it will not set it any faster, and may take forever to set and harden if at all. To speed up setting use gentle heat, and you can warm your mix up by putting your glass etc in a bowl of warm water for 3 min. Dont use expoxies below 10 degrees C, that will adversely affect curing too