P2NP: Appearance

These crystals should be pale yellow, however long term storage or travel at temperatures above 5 °C / 40 °F will gradually cause the crystals to change from a yellow to an orange and then a red colour, this is an increasing degree of product polymerisation from it's outer layer inwards.

You can easily remove the undesirable polymerised product, by rinsing with isopropanol (IPA) 99% or higher (see recrystallisation protocol).

Wearing butyl gloves (or 2 sets of nitrile gloves), place crystals in a PP or Pyrex/borosilicate container add about a third by weight of IPA, stir well for a couple of minutes, and then filter through your buchner funnel using a fast filter paper or mid-porosity frit (G3).
Leave the vacuum pump on for ten minutes after filtration to dry the crystals, then carefully transfer them to an air-tight PP container and place in a freezer until needed.
Viable crystals can be stored in a refrigerator (0 to 5 °C / 30 to 40 °F) for 6 months, or a freezer (-5 to -15 °C / 20 to 5 °F) for 2 years or more.
If you do not have a buchner funnel and vacuum source, then you will have to gravity filter, using beaker that a funnel can sit on, place 2 coffee filters and pour crystal and IPA mixture in, now place everyting in a refrigerator to filter and then dry before storing.

P2NP Appearance:

Cleaning crystals: