Cut a red-colored cocoa butter transfer sheet into ten 2-cm/.8-in-wide strips.
Place the strips on an acetate sheet large enough to hold all of the strips, cocoa butter side facing up.
Temper the white chocolate.
Spread the white chocolate over the surface of each acetate rectangle, spreading it evenly into a thin layer with an offset spatula.
When the chocolate has semi-crystallized, cut out 10 rectangles that measuring 6.5cm/2.6in wide by 10cm/4in long using a ruler and the back of a paring knife, making sure to keep a red band of the transfer sheet on one of the long sides of the rectangle.
Flip the acetates over onto a flat surface lined with parchment paper. Place a flat, heavy weight over them to help the chocolate set flat and not bow.
Keep in a cool, dry area, preferably enclosed. Discard after 1 year.