Sunday, 22 April 2012

More Glass Plates

Kodak O.250 Rapid Ortho Metallographic Glass Plates
Following the successful results exposing and developing old Ilford R.10 glass plates, I wanted to test another box, again previously opened. These are Kodak O.250 Rapid Ortho Metallographic Glass Plates and, according to the Early Photography website, Kodak's Rapid Ortho emulsion was only available in plates. These are 6.5x9cm plates, slightly larger than the imperial size of the Ilford plates (the small handwritten label on the box states: "Do not fit 3 1/2x2 1/2 single slides"). The box is also inscribed with a marker pen '28/6/62'. The plates in this box, unlike the Ilford plates, are wrapped in fours, with the central pair held together by paper runners. It wasn't clear which way around the plates were facing: whether the central pair were facing, and the other two facing outwards, which was the choice I made when loading the plate holders. This turned out to be the wrong decision, as the emulsion on the central pair faces outwards, the outer plates facing inwards. As a result, in the plate holders, the anti-halation backing faced the lens. I shot these plates at the same rating as the Ilford plates, roughly 12 ISO. The plates do not have a speed rating other than the name O.250, but looking at the information on Early Photography, it looks as though these plates may have been as slow as 16 ISO originally.

Kodak O.250 Rapid Ortho Plate, loaded back to front, shot in Icarette L
When I took the plates out of the holders in the darkroom under the safelights (these plates being orthographic) I realised my mistake. However, I went on to develop the plates, using the same method as the Ilford R.10 plates, using Rodinal diluted 1:100, stand developing for an hour. The results show that the anti-halation backing transmits enough light to give a fairly good image on the emulsion, but the backing wasn't a smooth, even layer (which I could see before developing), with the effect of creating mottled patches which also diffuse the focus in these areas. The negatives are quite thin but the plates are clearly usable, and perhaps shot the right way around the negatives would be sufficiently dense to use at 12 ISO.

Kodak O.250 Rapid Ortho Plate, loaded back to front, shot in Icarette L
Edit: 28/04/13

I recently bought another box of Kodak O.250 plates, and this had an information leaflet inside. It gives the speed of the plates as 8 ASA for daylight, and just 3 for tungsten, but it isn't clear whether the plates are from before or after the black & white speed rating change of 1960: if from before, then the original rating of the plates would have been 16 ISO. Either way, the plates have lost very little sensitivity despite being fifty years old. It provides filter factors and developing times for D61a and D76 (Ilford's ID11). The leaflet describes O.250 plates as being:
recommended for photographing biological sections, metallurgical and mineralogical work, spectography and macrography and clinical photography where neither red sensitivity nor high speed is necessary. It is also suitable for commercial, landscape and architectural photography and for studio portraiture by daylight.
Kodak O.250 Plate leaflet (front)
Kodak O.250 Plate leaflet (back)

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