Taking care

Taking care

I’m rather late posting (and indeed writing) my blog today – long agonising and thinking about care responsibilities now that I’m in Tier 4. And that links to an idea I’ve had for a while about darkroom procedures, O Level chemistry, and photography in general.

I had an inspirational chemistry teacher, Bob McDuell, who went on to write textbooks: I remember him for lots of things apart from the chemistry. His careful examination of a mark carved into the thick wax coating on one of the benches in the chemistry lab, and the way that he found it interesting that one pupil had exactly the same mark on his chemistry exercise book, for instance…

He had a forensic approach to examinations, and was the first person I was conscious of ‘question spotting’ – as part of our revision, he went through the areas that always appeared in the exam. Question 14 will be on nitrogen, and if you know these four equations, you will get 20% of the marks available for the paper. And in one lesson, he applied the same line of thought to how big a molecule is, and how many there are in a gram of a substance.

This was all based around setting limits: we didn’t get accurate figures, but we did prove to ourselves that molecules are very small, and there are a lot of them. Part of the experiment involved dissolving a gram of potassium permanganate (you know it – very bright purple, stains your fingers brown, pretty good for cleaning drains, but not very poisonous) in a litre of water. We then discarded 900ml, and made it back up to a litre. And repeated. And repeated again. The fact that the solution was still detectably purple meant that there must be at least one molecule of the chemical still in it: so 1 gram contains at least… I’ll let you do the maths.



Cleaning a test-tube involved swilling it out with distilled water three times – and every time I work in the darkroom, that’s how I clean my measuring cylinders and tanks. That’s the level of care that you need to avoid cross-contaminating your solutions, and the messy, mucky images that leads to. We used glass stirring rods because they’re easy to clean: wooden cooking utensils still make me a little bit uneasy!
But what level of care do you need for digital? How dry do you need to keep a lens that isn’t weather-sealed? And there are loads of questions about keeping a sensor clean…

The answer with the lens is simple(-ish) – very, if it’s electronic, but the part you need to worry about is the join between control rings and the body, not the hood, or even the front element. But if it’s a thoroughly mechanical device like my Leica lens, it’s far less of a problem. When you change lenses, hold the camera body with the front downwards, to minimise the chance of dust just floating down and landing on the sensor. And if you shoot a bright subject at a small aperture with a long lens and don’t see any dustbunnies, the sensor is pretty clean.