Polarizing viewer

Materials

• clear double-sided tape
• 2-ply mat board, Photographic Activity Test (PAT)^{Footnote 1} approved
• two polarizing filters/films (H10.5 x W10.5 cm)

Tools

• scissors
• ruler
• Exacto knife or mat cutter

1. Cut four pieces of mat board to external dimensions: H 18 x W 18 cm
2. Cut four inside windows within centre: H 9 x W 9 cm
3. Cut two polarizing filters/films: H 10.5 x W 10.5 cm

1. On two mat boards, place a piece of clear double-sided tape above each side of the centre openings.
2. On two mat boards, place the polarizing filter/film on the double-sided tape to cover the centre opening.
3. Tape the two mat boards with the polarizing filters/film to the two remaining mat boards.
4. Together these make the polarizing viewer.

1. Place the two mat boards with filters on top of each other. If the filters/films are transparent, they are not polarized.
2. Turn one mat board with filter 90 degrees.
3. If the filters/films are opaque or black, they are successfully polarized.

1. Using gloves to handle the negative, place it between the two polarizing filters/films that are in polarized orientation.
2. Hold the polarizing viewer firmly together to prevent the negative from slipping out.
3. Observe the thinnest possible density of the negative through the polarizing viewer (the outer clear edge is a good choice) while gradually tilting it.

4. If a rainbow^{Footnote 2} pattern becomes visible, then the negative support is polyester.
5. If no rainbow colours are visible and the polarizing filter/ film remains black, then the negative is on an acetate support.