Last weekend I cut and edged my glass plates. To ensure that photographic emulsion adheres to the plates through all the processes involved in developing an image, the glass must be free of any coating applied during it’s manufacture.
There are various methods of cleaning that might be used, from detergent to acid etching. I chose a middle course of soaking the plates in a strong detergent solution followed by scrubbing with wire wool scouring pads and sugar soap wipes. After rinsing with clean water and leaving them to air dry I gave each plate a final clean with isopropyl alcohol.
This weekend I set about subbing the plates. The purpose of subbing is to ensure good adhesion between the hard, smooth surface of the glass and the relatively soft, delicate layer of photographic emulsion such that the emulsion will not lift during processing.
I made up a solution of gelatin dissolved in hot water to which was added chrome alum as a hardening agent. The prepared subbing solution was kept at a temperature of around 45ºC by water bathing both the mixing jug and the tray in which the plates were to be immersed. Once coated the plates would be allowed to dry completetely before being packed together for storage with pieces of baking paper between them to prevent sticking or damage.
With my plate rack set up on the draining board and my coating tray in a water bath in the kitchen sink I set about the task of dipping each of my cleaned glass plates in the subbing solution. Once dipped, I held each plate up to allow the excess to run off before placing it in the rack. As I held the plates up I became quite aware of the individuality of each one. Small marks in the glass, whether imperfections in manufacture or as a result of the laborious cleaning process I had opted for, glinted in the sunlight coming through the kitchen window and little gelatinous bubbles were forming as the solution thinned out and began to dry.
Having been hand cut, the edges and notch of one plate differs from the next, the manual cleaning process had placed marks unique to each on the surface and now the subbing solution was adding a further layer of individuality. In the final stage of preparation, hand poured emulsion will complete the unique individual character that each plate will give to the image that will be made on it. It will be interesting to see the interaction of these plate ‘imperfections’ with the action of light on the emulsion during an exposure.
The subbing will harden over the coming days and the plates should be good to store indefinitely, not that I intend to keep them that long! I’m keen to put them to use but I will give them a week or so before coating with emulsion. Even then, the coated plates will need to dry for at least twelve hours before use and from what I have read elsewhere the sensitivity to light of the emulsion will improve if left for a few days after coating. But all that is for another day, in a week or so.