But how do you know if you've properly exposed and developed your negatives? Well, that's exactly what this simple test is designed to tell you.
To produce a good print you must start with negatives that make it possible. Your negatives must be accurately exposed and developed so that they contain a density range that matches exactly the contrast scale of the paper you use. For example, if your standard paper is Ilford Multigrade with a No 3 filter, which gives a contrast scale of 10:1, then the density range of your negatives - excluding clear film and solid blacks - should also be 10:1. If it's more you'll lose either shadow or highlight detail. And if it's less you'll produce flat, muddy prints.
To ensure that all tones are correctly reproduced in your print you should give the minimum exposure possible consistent with retaining adequate shadow detail. This means that any object in your picture that you want to appear as solid black in the print should be represented by clear, unexposed film. Any shadow areas in which you want detail will then appear as slight densities in the negative.
Place a sheet of your usual paper on the enlarger baseboard and make a test strip in the usual way, giving exposures in two-second steps. Try to give ten two-second exposures to produce a test strip with exposures from 2 to 20 seconds.
Process the test strip exactly as recommended by the manufacturer, at precisely the right temperature. When it's dry, take it into good light and find the first step that's a full black. The step before it should be a very slightly lighter grey and all the steps after it should be the same full black. Check what exposure produced this step. Let's say, for example, that it was 16 seconds.
Make a note of the enlarger head position on the column scale. Or use a felt pen to mark the enlarger column. This is your standard 8 x 10in print position.
On the back of the test strip write the make of the paper, its grade, the aperture at which the enlarger was set, and the exposure that produced the first full black step. Also write the type of film that you used for this test.
What you've done is to establish the minimum exposure you need to produce a full black tone on your usual paper. This becomes a standard exposure time for all prints you make at this particular degree of enlargement and lens aperture from the type of film you used for the test.
If all's well with your technique your print should be perfect. It should show plenty of shadow detail, full blacks, luminous highlights and the odd pure white. But if your technique needs overhauling, your print won't be up to scratch.
If your print is generally too dark with a lack of shadow detail and large unrelieved black areas, your negative was underexposed. Make prints from a few other negatives in the same way: if they're all too dark, rate your film at a lower speed in future.
Don't make the mistake of thinking you can solve the problem by reducing the print exposure. Because the exposure you've given is the minimum necessary to produce a full black, reducing the exposure will only result in a print with no real blacks. If, on the other hand, the print is too light - with burned-out highlights and no real blacks - your negative has been over-exposed. Again, check the results by printing other negatives on the same type of film and if they're also too light rate your film slightly faster in future.
If the shadow areas of the print look good with plenty of detail, but the highlights are burned-out and lack detail, the negative is too contrasty for the paper grade you're using. And since high contrast is produced by over-development, you'll need to cut your development time. Try a 25% reduction for a start. Alternatively, you could stick with the same development time and standardise on paper a grade softer.
Finally, if the shadow areas are about right but the highlights are too dark, the negative is too soft for the paper you're using. This means that you should increase the development time by perhaps 25% to give more contrast - or you could try using a harder grade of paper as your standard.
One final point, though. If you use several different types of film you'll need to carry out this test for all of them. This is because different types of film have different base densities, so what produces a full black with one film may only produce a dark grey with another.
Once you can produce technically perfect prints consistently, you have the foundation on which to build your pictures. You can forget technique - because it becomes second nature - and concentrate on what really matters. Your pictures.