Teach Soap

I am a newbie to soap making and have 2 separate questions:

1. First, do the melt & pour bases have an expiration time? I hope they are usable for at least a year.

2. Second, I've watched many videos where the M&P bases, butters etc are weighed on the scale while sitting in a pyrex.
If we are measuring to very precise measurements, some a fraction of an ounce, doesn't the pyrex itself add weight to the ingredients?
How is this accounted for in the recipe or do you use wax paper?

Thanks in advance

Most MP suppliers put an expiration date of 1 year on MP bases. Not that it goes bad if you don't use it exactly within a year, but it can lose some of the glycerin.

When you're weighing your ingredients in something, you're going to want to put the container (pyrex or whatever) on the scale first & then push the "tare" button before putting your ingredients in the container to weigh them.

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Genny