Ilford G.30 Plates

Ilford G.30 Chromatic backed plates

Following the first vintage glass plates I shot last year, I've been keen to use more, although I have only found time to do so recently. I bought a couple of previously unopened boxes of Ilford G.30 Chromatic glass plates in 4x5 size; one of the film holders for my MPP large format camera takes glass plates (it does also have film sheaths, which can be inserted to shoot film). As the label states 'Open in red light only', the word 'Chromatic' appears to mean orthochromatic; where the label continues onto the underside of the box it also states, "Meter settings for minimum exposure ASA 10 DIN 11". The design of the packaging suggests the plates are from the 1960s; the leaflet inside the box has a code number L.64/D, which might refer to the year of printing, 1964.

For the first test I metered for 10 ISO, and took three successive exposures on the same plate, progressively withdrawing the darkslide between each shot (although not very evenly). Viewed from left to right, this effectively achieved exposures indexes of 10, 5, and 2.5. The plate was stand-developed in R09 One Shot (Rodinal), at a dilution of 1:100 for one hour, with a couple of inversions at the half hour mark.

Ilford G.30 Plate test - three successive exposures at 10 EI

There is some blurring due to a small amount of movement between the multiple exposures, but in terms of a test to determine a working exposure, it's clear enough. The first exposure at 10 EI appears to be workable, and initially I did think that this might have meant that the plates hadn't lost any sensitivity over the 50 years since manufacture, but Flickr member richard314159 reminded me of the doubling of film speed by the ASA in 1960. This change in standards simply reduced the margin of error against under-exposure. Although I can't be sure that the plates are from before the revised ASA settings, if so the plates would have originally been 20 rather than 10 by modern standards, and so may have lost one stop in sensitivity. There's also not much background fog on this plate, probably not much more than I've got with some contemporary films; from my limited experience, slower emulsions do appear to age better.

I subsequently shot two plates at night with long exposures. On first inspection, these seemed like they might have been over-exposed, but, particularly with the second plate below, this was important to register the foreground detail, although at the expense of the clarity of the lit-up lettering. The haloes around the lights are somewhat unusual, this may be due to the fact it's shot on glass. It is also noticeable that there's a line of thicker emulsion at two of the adjacent edges where, as it was poured onto the plate, the emulsion collected as the excess was poured off.

Ilford G.30 Plate - 1 minute exposure at f5.6

Ilford G.30 Plate - 2mins exposure at f5.6

Edit: 29/04/13

As a result of my research into Ilford, I discovered the Ilford Technical Information Book, which contains a sheet on the G.30 Chromatic plates, dated to 1965. This provides additional information for the plates from the leaflet in the box. It describes the G.30 Plate as

widely used for the photo-micrography of metal specimens. It is particularly useful for green-corrected microscope lenses since it allows comparatively short exposures to be given when using a Tricolour Green filter.

Ilford G.30 Chromatic Plates are used in the graphic arts, copying and scientific fields. For graphic arts work the main use is in the preparation of continuous tone negatives.

It gives the ASA setting for tungsten lighting as 5, against the daylight setting of 10. The date of the technical information sheet disproves the idea above after my first test that the meter settings were from before the change in speed ratings for black & white emulsions, and so the plates have lost very little sensitivity since they were made nearly 50 years ago. The table of development times gives further dilutions and times for both continuous and intermittent agitation.

Ilford G.30 Chromatic Plate development times

Ilford G.30 Chromatic Plate sensitometric curves

I subsequently shot some more plates with my MPP Micro-Technical camera, the best of which is below, a difficult subject given the brightness of the fluorescent strip lights under the awning compared to the building above.

Ilford G.30 Plate, 12 seconds exposure at f4.5