Spreading Butterflies: The relaxer. Dried, papered butterflies must be 'relaxed' (humidified) to make them supple before they can be spread. I use a plastic container with a tight-fitting lid. I put a layer of wet paper towels on the bottom. Important: add a fungicide to prevent mold from growing on the butterflies. I use a few drops of Phenol (carbolic acid) that I purchased from a pharmacy. Use caution: Phenol will burn the skin. On top of the paper towels I lay a piece of plastic to separate the butterflies from the towels so they don't get too wet. I do not take dried butterflies out of their envelopes until the second day of relaxing; to avoid the risk of breaking their antennae. After the first day or so I will remove them from the envelopes and put them back in the chamber - to speed up the hydration process. It takes about a week to fully relax dried specimens. More or less, depending on their body thickness. It is important that your lid fits tight so that you can create 100% humidity within the relaxing chamber.
All that being said, it is much easier to spread fresh-caught specimens. To avoid the relaxing process for fresh-caught specimens, never let them dry out. Whenever possible I store my fresh-caught specimens in field envelopes and keep them in an airtight container until I get home from a collecting trip. Then I place the envelopes inside a Ziplock bag and put them in the freezer. When I am ready to spread them I just take them out of the freezer and thaw them out. The thawed specimens retain their original suppleness thus making the relaxing step unnecessary. I have sucessfully stored frozen specimens for up to six months in this manner.