To protect a friable artwork, carefully lay it, face down, on glassine paper. Glassine paper is a transparent, resilient glazed paper that is resistant to passage of air and grease. It may look and feel like wax paper but never use wax paper for this purpose as the wax layer may melt and damage the artwork instead of protect it. Make sure to cut the glassine paper at least 1/2 inch larger than the artwork.
Gently fold the edges of glassine paper over the sides of the artwork, creating sharp creases all around but taking care not to press on the painting too muck to avoid smearing or smudging. Use painters blue tape to secure the folded corners of the glassine paper, making sure that the tape does not stick to the back of the artwork.
Cut to size two pieces of sturdy and thick cardboard stock. The cardboard must be at least 1/2 inch larger than covered artwork in all directions. Lay the cardboard pieces side-by-side and attach the sides with tape so that the boards will open like a book.
Place the artwork, face up, on top of the right-side piece of board. Flip the left board over so that the artwork is “sandwiched” between the two boards. Carefully seal the remaining three sides with tape to secure the artwork inside.
When shipping multiple paintings of the same size, you may just add “leaves” of cardboard into the “book” and insert the glassine-covered pieces between the boards. Secure the sides with tape.
Insert the boarded artwork inside a clear bag. Seal the bag with tape. Fold over and tape if the bag is too big for the artwork. Bagging will help protect the artwork from moisture.
Pack the artwork depending on its size. A padded document mailer can be used for a small piece. Larger pieces can be boxed, just make sure to surround with ample cushioning such as bubble wrap to prevent movement.
Seal the package with tape and label accordingly. Use the fastest service you can afford to minimize the time it takes the item to get delivered and lessen the risk of getting damaged.