Jon Hilty
Silver Nitrate Doser
 A view of Random RoadThe normally black asphalt turns white in this process! |  A view from the kitchenThe paper is darker due to it still being wet -- the dmax is slightly decreased upon drying. A chain accidentally brushed the emulsion after development, which unfortunately left a mark. |  A view from the beachThis is a view from a beach area on a small lake. The object in the middle is a dock used for swimming. The white "beach chairs" only show up here as silhouettes, and the tree line across the lake is similarly absent. This picture required nearly 4 hours of development before a discernible image could be seen! |
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These photographs were made somewhat similarly to the standard Gum Bichromate process, differing in two ways:
1. The gum solution utiized white gauche on black paper instead of darker pigments on white watercolor paper
2. The gum papers were exposed in-camera, rather than contact printed with a negative.
I designed this little dosing machine to control the rate at which silver nitrate is added to a photographic emulsion during the precipitation step. It's basically just an Arduino running a dual-H bridge, that controls the speed of a peristaltic pump via PWM. It offers a few different features -
Auto Mode: The user can set a desired flow rate, number of doses, and (if desired) pause times between doses
Manual Mode: The user can use the knob to control the rate of the motor, by varying the PWM output from 0-255. The screen displays the estimated flow rate.
Purge: This just runs wide open for a user-defined period of time. Useful for cleaning out the tubing afterwards.
