I got this tip from Annette and she was nice enough to give me permission to share it.
Float off used postage stamps for collage or backgrounds
by Annette Warkentin
Float used/canceled postage stamps off envelopes by placing the stamp face down in warm, soapy water. Wait a minute or two and the stamp will float off the envelope. Dry between weighted paper towels. Your canceled stamps are ready to use in collage or to make a montage, scan, print and use as backgrounds. Be sure that the scanned stamps are not complete so copyright laws are addressed. Overlap the stamps a bit, be sure the canceled portion is visible and if in doubt, go to the USPS website to check out their policy.
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