I suppose you could get away with it, but why take the risk of something going wrong just to save a couple-o-bucks and a few cups? BTW ... the rule in my shop is ... "If it's gonna go wrong, it's gonna go wrong on the deck!".

I use 8 oz. clear plastic cups. I fill a few of 'em up with resin before I start glassing. As I glass and use up the current cups epoxy, I just add the hardner to the next cup and continue on. True, I used up about $6 worth-o-cups for the complete project ... but nothin' went wrong 'neither!

Ken