Wrap the artwork in acid free tissue paper to protect it from abrasion and the harsh chemicals used in many commercial paper products. A few sheets on both sides should suffice.
Cut two to four pieces of cardboard and place the artwork between them and centered. This rigid housing protects the artwork from bending. Tape the edges of the cardboard to prevent them from separating and the artwork from sliding out.
Set the artwork in a box and fill the excess area with packaging peanuts or bubble wrap until it is secure. Close and seal the box with packing tape.
Wrap the artwork with acid free tissue paper and then with a shipping blanket.
Line the bottom and back of a mirror box with bubble wrap and place the painting inside. Use extra bubble wrap for the corners to protect the most fragile part of the frame.
Use more bubble wrap or blankets to protect the exposed edges of the painting as it sits in the mirror box.
Place the other piece of the mirror box partially over the one containing the artwork and fill all excess space with Styrofoam peanuts, foam inserts, bubble wrap or other packing materials.
Seal the mirror box and secure it with packaging tape