Friday, 20 December 2013

Paper Flashing the pre-flash.

High contrast negative
printed normally.
After my last post you maybe wondering if this is going to be saucy, you will have to read on to find out.

Types of flashing:

Paper flashing is divided into two types, 'pre' which is done before the negative is exposed to the paper and 'after' which is known as fogging. This article is going to deal mainly with the former as it is a good way of controlling the contrast of hard to print negatives and adding a finer quality to others. It is also the one I have used most often.

How it works:

The first thing to do is explain how pre flashing works. All photo sensitive papers have a built in inertia to light, this means that the paper has to absorb a certain amount of white light before it starts to tone or show detail. When a paper has been pre flashed and the negative is exposed, all the light shining through produces tone and detail, because of this the amount of exposure needed is reduced, in some cases by 20%. This makes the lower values less likely to black out producing better separation in the shadows. It also affects the other end of tonal scale - the highlights, which receive more light, improving the detail and tone being recorded. With the inertia overcome, all the light passing through the negative is working on producing detail and tone. A consequence of this is a lowering of contrast making a finer balanced print.
Print after pre-flash

When to Flash:

Since flashing is a way of fine tuning contrast, it can be used to produce half grades with fixed or variable contrast papers. You do not have to flash to the maximum but can use it incrementally up to the point of tone. You do not have to flash a whole sheet of paper, it can be helpful where a sky in a scene is over blown to just flash that part of the paper. This is done by Dodging (holding back) with a piece of black card the other section of the paper preventing it from receiving any light. Remember that you should keep the card moving otherwise the final picture will have a black line going across it. Most negatives will not require flashing. If used inappropriately it can produce flat and unnaturally long toned prints. So be selective in your approach.

If you're a split grade printer you should not be afraid of pre flashing the paper as it has no adverse affect on this method, but can aid the production of better photographs.


Your enlarger and a reasonable accurate timer. For those who have the space you can set up a second enlarger just to do flashing or you can use a paper flasher by RH Designs.

How to Flash:
The main thing to note about flashing is the method you use has to be precisely duplicable so you can reproduce predictable results time and time again. One method is to set the enlarger light box at maximum height and close the lens down to minimum aperture (F16) with a timer connected, timing the segments at intervals.

For those who don't have a second enlarger things become a bit of a pain having to move the light box up and down like a yo-yo during the printing process. But there are ways round it. You can batch flash your paper keeping it in a separate box but only produce enough for that printing session. Secondly, find your own method of flashing which is what I have done. I move the light box to a height where the light from the lens covers an area larger than the paper I'm using, which is slightly higher than what I would use for printing (don't forget to make a note of the height for future reference). Set the lens to F8 and then time the segment at tenths of a second. You can increase the timing by closing down the lens. Don't be afraid to experiment to find a method to suit. You can do all this with the negative in the carrier and use a diffuser under the lens that scatters the image enough not to make an impression on the paper, but this can lead to overly long exposure times.

Making a test strip:

Test strip
The method is the same as making a test strip for printing a negative. You need a strip of light sensitive paper and a piece of black card so you can expose sections incrementally. The only difference is you will need to mark the test strip with a pen so you can see how many segments have been exposed before the paper starts to tone. The paper is developed in the normal way. To check the test strip properly it needs to be totally dry to allow for dry down tones that may appear in segments that look clear when wet. You can force drying by using a hair dryer or the microwave. If you use several sorts of paper the test should be done for each and then stick the results to the front of the box for reference. It also means that each new box you purchase will need a test, as each new box is a different batch.

Exposure curve.

This simplified exposure curve shows what happens to photographic paper when introduced to white light. The lower part of the curve marked 1-3 is the area of 'inertia' when exposed for this short period of time and then developed there would be no change in the tone of the paper. When timed to 4 and developed there should  be the first signs of tone 4a. If you then time it to 5 at the top and develop it, it would be maximum black. (also known as D MAX) to add any more time after this point will not make the paper any blacker than black.
Flashing is about giving the paper just enough white light to get it to 3 before you expose the negative to extend the tonal range. Further white light from this point 3 is a different type of white light known as fogging.