Put a few drops of the fragrance onto a cotton ball.
Put up to 15 cards and the cotton ball in a large ziplock bag, close and let it sit for at least 24 hours. Take care not to let the oil come in direct contact with cards or envelopes as the fresh oil could stain them.
For tissue paper, follow the same procedure, but place the cotton ball into the plastic package of tissue paper. Be careful not to let the oil come into contact with the paper. Close the bag up and allow to sit for 24 hours.