Figure out the dimensions before purchasing your materials. If your Egyptian painting is 30 by 20 cm, then you need a frame that is 35 by 25 cm or larger. Your mat board should be just as large as the frame or a bit larger, unless the frame is wood boarders and glass in the middle. If the frame you choose is all glass, then purchase a mat board that is 5 to 7 cm larger than the painting.
Secure the painting to the mat board with the sticky tack. Measure 5 to 7 cm from the side and top of the mat board. Set the painting on the mat board with a 5 to 7 centimeter gap on each side and on the top and bottom. Draw lines with a pen, pencil or white-out pen in order to know where to cut. If the frame is larger than this and not all glass, then cut the mat board to fit the frame and center the painting on the board.
Use the razor blade to cut off excess mat board.
Frame the mat board. Use the sticky tack to secure the mat board to the frame if needed or desired.