Little Windows formulas are pure and safe, but as with many epoxies, the shelf life on your Part B is about 1 year, if stored properly. Once it starts to change color, it will still be functional well beyond that time, but it will be better used in projects that don't require the crystal clarity, so save it for Dichro-ISH, adding glitter, fabrics, dyes, powders, or other elements, where the clarity isn't crucial. If you're working on photo pieces, it will be best to use fresh product. We offer replacement bottles of Part B, or new sets in different sizes.
Here is a link to our resin sets and Part B replacements.