The Becquerel Process in Detail:

When the plate is exposed to iodine vapor it immediately changes color. To view the color, use a bright light onto a white surface or the wall and view the plate as it reflects the white surface. First, a pale yellow, then a darker yellow and a sequence follows that progresses through the natural color spectrum--orange, red, purple, blue, green then back to yellow. The first cycle colors are very pastel and the blue and green almost appear clear or slightly grey. Also, they blend together some and have an iridescent quality. The following color patches, photographed from an iodized plate, give an approximation of the colors at five steps. The first is a yellow that is shifting to orange. In the second, the shift is more to red. The third is a purple, the fourth a blue, and the fifth a green.

The second cycle colors are much more saturated and easier to identify.

A couple ounces of iodine crystals in the fuming box at around 70 degrees F should be adequate to reach the first cycle red purple in 20-30 seconds and second cycle colors in 2 or 3 minutes. A colder box will take much longer. Also it is a good idea to warm the plate before sensitizing for a more even coating. After the correct color is achieved and with a safe light on, put the plate back over the iodine for a few seconds. The erases any effect of room or viewing lights. Store the sensitive plates in a cool place and they will be good for weeks.

Any of the colors of the first and second cycle work and will make daguerreotypes. The first cycle colors will give images more contrast with deep blacks and as the layer gets thicker, the contrast abates and more tones appear in the mid ranges. This test plate illustrates this phenomenon.

My best results have come from the reddish purple of the first cycle and the magenta, purple, and green of the second cycle.

Examples of fuming boxes