When Fog attacks

When Fog attacks

Recently my tintypes have been plagued with relentless image fog. For the last month I’ve not had many useable plates. I have stopped shooting with models and my photography is at a standstill.

Incase anybody reading doesn’t know the tintype process, basically its this. Coat a black aluminium plate in photographic collodion by pouring it neatly on top and letting it set. In the dark place this plate in a bath of silver nitrate. After a few mins remove the plate, load it into a camera film holder. Place the film holder into the large format camera, take your picture. Go back into the darkroom and pour developer onto the plate. Pour water onto the plate to stop development after roughly 15 seconds (you determine this exactly by sight using a red light as you can see a negative image on the plate building up in density, develop for a second or so longer and you will get fog) You then place the image into fixer solution and it magically becomes a positive, light proof image.

Problems started when I switched to a new bottle of collodion halfway through a shoot. Now it would be easy to jump to conclusions that the collodion is to blame, there is some truth to that. New collodion is more sensitive than old collodion. However it should be possible to get new collodion to work with some adjustments. To test the collodion I have since tried a second mix of collodion with identical results which tends to indicate that the collodion is probably OK.

New collodion combined with a new silver nitrate bath is probably the worst combination but sometimes its just inevitable. Pouring some adged collodion into the new collodion could help control the oversensitivity, thus reduce the chances of image fog. Ive yet to try this as I’m a bit worried it may make the plates under sensitive if I get it wrong. Also if I start of too delicate with my addition of old collodion it may take a whole day to calibrate the correct amount and thats assuming it will fix my fog issues.

Silver Bath
My silver bath is fairly new and shouldn’t be the issue. My gut feeling is that if anything is wrong with the silver bath, it would be the acidity level of the silver nitrate solution. Testing requires PH test strips. After playing around with two brands of test strips ive come to the conclusion; I do not know how to use them, or their accuracy is all over the place between suppliers. I resorted to purchasing a digital PH meter. I have yet to test the bath, adding acid into the bath should reduce fog but will result in longer exposure times in camera. The ideal PH is 3-4.

During a recent workshop with Mark Osterman, it was hammered into us that you should sensitize your plates in the silverbath only as long as necessary and no longer. This is determined by pulling the plate out of the sliver bath and observing for streaks of liquid running down the plate. Once these streaks stop forming and the silver flows off more evenly like a sheet of fluid its time to take out the plate.

Recently the streaking seems to stop after about 2 mins, whilst I’m used to sensitizing for 3 mins. This could indicate the chemistry is a little hot and I need to make sure I do not over sensitise plates in the bath as this can increase the chances of fog.

Im finding my plates are developing too fast and I believe this is the main reason for the fog. In order to try to control development it is useful to understand very basically how developer works.

Developer is fairly simple, it is Ferrus sulphate (iron), Acetic acid, alcohol all diluted in distilled water. Iron is the key ingredient, when the iron is poured onto the plate and agitated. The Iron searches out the exposed areas of the plate and builds up the image density making the image visible. However this reaction would be too rapid and uncontrolled with Iron alone. The image would appear up at once including areas of deep shadow. Fog would result all over with little separation between tones.

In order to control this reaction, acid is used. Acid is a restrainer, it slows down the action of the iron. This allows the photographer to stop development before the plate becomes too dense all over and fogged whilst building up the tonality of densities in a more controlled fashion.

As well as adding acid, ferrous sulphate can be reduced although acid always needs to be present. Another method is to add an organic restrainer like sugar. This increases the viscosity of the developer so that the Iron takes longer to react with the plate. Recently Ive been adding more acetic acid with little effect. It started to become frustrating when even doubling the acid had little effect. I knew this shouldn’t be the case. I started to become suspicious of my acetic acid. I was right, My glacial acetic acid is not glacial at all. This seems to be a common problem with chemicals from ebay, never believe the label.

I obtained more acid and this time I could tell it was different, it stank of nuclear powered vinegar, 8000% more stincky than my older batch. In fact, I almost died and I found a good mask asap. It also froze below room temperature as it should. Eager to test out my new developer I made some more plates and….. they all fogged.

That night I had trouble sleeping as it was too hot, all of a sudden it came to me, its too bloody hot. The heat would cause the Iron to act more aggressively. It would also cause my development times to vary from day to day. I was really getting to grips with tintypes in the winter, now its the summer and its all screwed up.

Armed with this new info, my new plan is to reduce the temperature of my developer. I feel the standard published developer mix is probably by and large the sweet spot for good images. Messing around with the formula starts to overcomplicate everything. I feel if I keep my developer formula exactly the same and simply keep it in a cool box, I may have a more consistent approach to making tintypes during the summer. Failing that a the addition of a little or lot more acid my be the next plan of attack. Watch this space and keep all fingers crossed for me.