When you buy a safelight thats exactly what you expect it to besafe! The truth is a safelight is only safe if used with certain papers and with the right bulb, at a safe distance and for a certain processing duration.
If you have the wrong combination your prints will be fogged by the safelight and quality will be degraded. This is often not fully apparent and would only be noticeable when you compare an unfogged print by the side of a perfect print. Fogging basically introduces additional exposure to the print making whites appear grey and this increases as the safelight conditions are reduced. Theres an easy way to test your safelight but before we show you lets look at each factor to see how we prevent fogging.
The first thing is the colour of the light. Choosing the best safelight is essential if you want maximum brightness with the safest light. The colour of the light output controls this and these can generally be split into four colour groups: Red, Orange, Green and Brown. Each is designed for different kinds of papers and again in rough categories Red is suitable for orthochromatic and lith products, which have a wide sensitivity, Orange is perfect for most standard black & white materials and Brown is for the multi-contrast materials. Colour materials can be processed under Green light, which delivers a minimal amount of light making it possible to find your way around the darkroom, but the room will be dark enough not to fog the paper. Theres one other less common category for colour and that uses a Sodium light source which is much brighter than green, but the downside is its far more expensive to buy and replace bulbs.
You may have the right type of light but when you replace the bulb you could have inserted the wrong one. Most lights require a 15w bulb but it would be quite easy to buy a more powerful 40w model the light would be the same colour but it would be brighter to see, and that also means it would brighter to fog the paper too! Always stick with the recommended illumination. Some DIY shops sell a red bulb that you may be tempted to buy. The trouble with these is the base of the bulb is not coated and leaks tungsten light out which will affect the results even though the room appears o be bathed in red.
Next we have distance. Check the specification sheet of your safelight and it will probably say use at a distance of one or two meters. Many darkroom users have their safelight positioned over the set of three trays and Ive worked in some darkrooms that dont even have one meter of space free! We dont all have the luxury of space and if you fall into this category dont worry yet our test will determine whether you are okay or not.
Our final problem is the length of time the light sensitive material is exposed to the safelight. This is from the moment you take the paper or film out of its black wrapper until its had about 30 seconds in the fixer.
So lots of things to affect your results and the easiest thing to do is to test your safelight and working conditions to see if you are fogging your photos and this can be done at minimal expense.
The easiest method is to lay a coin on a sheet of unexposed paper and leave it in the room in safelight conditions for about eight minutes, which is more than enough time to allow for a print to be made. Then, when processed, if the area where the coin has been is lighter than the rest, the safelight is fogging the paper or the room isnt light tight. Doing the same test first with the safelight off will test the rooms black-out effectiveness.
A more thorough safelight test follows:
1 Adjust the enlarger column so that its at the highest you would have it in normal conditions. So if you normally print 5x7in and 10x8in adjust it to the 10x8in setting and then remove the film from the negative carrier.
2 Make a test strip to determine how long the exposure would need to be to produce a very light grey tone.
3 Now, with the safelight in its usual working position, cover half of a new sheet of printing paper and expose the uncovered half for the length of time discovered in step 2.
4 Lay a sheet of card on top of one of the processing trays and lay the exposed paper emulsion side up on this.
5 Lay a steel rule or similar object down the centre of the paper to cover the middle strip and, using a sheet of card larger than the whole paper, cover all but a sixth of the paper and leave this strip exposed for one minute.
6 Move the card down to reveal the next sixth and leave for two minutes.
7 Keep repeating this doubling the exposure time as you move the card to reveal more of the paper.
8 Turn off the safelight and process the sheet.
9 You will now have a print with a series of progressively darker grey strips on the side that was exposed under the enlarger, a light grey clear reference strip down the centre (at the predetermined step 2 tone) and maybe a couple of light grey strips on the side that was covered under the enlarger.
From this test you can see how long you can handle the unexposed paper in safelight conditions and similarly how long once its been exposed.
If the time it takes to fog the paper is longer than the overall time it takes from taking the paper out of the packet, exposing it under the enlarger and developing it, you have no need to worry. If the fogging occurs on a strip within your printing process time you need to look at moving the safelight further away from the trays or buying a new more appropriate model.
If your safelight is fogging paper and you cant get it further away from the processing trays you could try wiring in a dimmer switch to turn the brightness down.