Micrographs of Precipitation Nozzles
One of the perks of being at GEH is the conservation lab. Not only do they have a bunch of awesome microscopes, but they have people that know how to use them!
Mark Osterman brought in a couple of old Polaroid precipitation nozzles (needles for introducing silver-halide into the emulsion pot) and I wondered how big the openings were. I asked Ralph Wiegandt if he could measure them somehow and he showed me how to do it on the microscope. These are at 50x.
There are 3 images; two metal nozzles that were originally used by Polaroid and a glass nozzle, hand pulled by Mark that we use in the emulsion lab here at GEH. The metal ones measure 0.6mm and 1.2mm; the glass one is also (miraculously) 0.6mm.
In hypodermic needle gauges, this translates to 16g and 21g.
To me, this brings up an interesting quandary. The same quantity of silver-solution can be introduced into the gel/halide "pot" in a set amount of time, yet the nozzles can be bigger or smaller. The effect being, to increase the pressure at which solution enters the pot.
On one hand you can have an incredibly fine stream of high pressure going through a very small nozzle, and on the other hand you can imagine a large nozzle that just "drips" out.
So how important is the nozzle size and the pressure?, or is rate of addition the more important factor??