The combining of several photographs into a single image can be accomplished in a number of different ways. Mainly of the early 'photomonteurs' such as Hannah Hoch. favoured the use of a pair of scissors, pasting down the often roughly cut scraps onto a more substantial background. A similar assembly method can be applied to photograph, although for more accurate cutting, particularly long the edges of objects, a scalpel should be employed. Many pre-computer advertising photomontages were made in this way.

The joins can be made less obvious if the edges are cut away underneath to give less of a step, either by careful use of the scalpel or scraping or using sandpaper (more effective with some papers than others.) Considerable retouching using a fine sable paint brush may be needed, one reason why rough surfaced fibre base papers - on which you can apply grey water colour or gouache - are often preferred for these procedures. If a truly seamless result is required you need to photograph the retouched print (take care to use diffused frontal light to avoid any shadows from paper edges).

All this of course is much easier digitally, and most image processing software will come with tutorials or help files that cover the joining and compositing of images. More adventurous photographers with access to a darkroom may still prefer to combine their images there, using two basic methods, multiple printing and the use of multiple 'sandwiched' negatives in a single printing exposure. Multiple exposure in the camera still has its uses too.

Sandwiching works best for negatives with large light or clear areas which allow the image from the other negative to print through. For example by photographing a person against a black background on several negatives you can then place two of these together in the negative carrier to make a print. If the two negatives are placed emulsion to emulsion in the carrier, then it is possible to get both acceptably sharp; if both are the same way up, then the two images are separated by the emulsion thickness, and by focusing on one. the second will be slightly out of focus. Either you can make use of this or you can attempt to render both acceptably sharp by focusing between the two.

Negatives intended for this use can be given slightly less exposure than normal (perhaps half a stop) if there is significant overlap between the two images, however normal exposure does not present any problems, and is probably best in that it also enables normal prints to be made. However if you intend to sandwich more than 2 negatives you should reduce exposure, or preferably, give normal exposure and reduce development times to cut the maximum density. Unless you do this you can end up with some very dense highlight areas that will give white areas on the print. For all work with printing from several negatives, variable contrast paper is recommended.

Multiple printing - using two or more negatives one after the other - allows much more control and also works differently. Having a darkroom with several enlargers makes life much easier - otherwise you will waste much time exchanging and setting up negatives, and accurate work is very difficult. If you want to combine several portraits of the same person you would start by taking them with a white background, so that the negatives are more or less opaque in these areas. For smaller objects the best solution - as advocated by Jerry Uelsmann - is to photograph them on a light-box.

Probably the best starting point is with a negative with a large area of high density - such as a light sky in a landscape with a fairly straight horizon. After making the first exposure from this (at the time to give a print normally) you then simply expose to the second neg, keeping the area below the horizon from receiving any exposure by holding your hand or a card roughly midway between the enlarging lens and the paper. It may help to stick some masking tape to the edges of the enlarging easel and making bold marks on this at horizon level to act as a guide. Don't worry about exact masking - you need a diffuse blending between the images rather than a sharp boundary.

Having achieved results in this way you may want to try other blends using a similar technique. Surprisingly good results can be achieved by skilled printers using just their hands to shade areas where exposure is not required, and normal dodging tools - card or cotton wool or another materials held on fine but rigid wire (one free source of this here is used fireworks 'sparklers'). So, to add a face in the centre of a oval mirror (or to a TV screen), I shade the mirror for most of the exposure time, moving a small oval dodger around slightly and also closer towards the paper during the exposure. Moving the paper to the enlarge with the face negative then print into the same area using either a card with a small oval hole, or through an oval made with my hands. Again the card or hand are kept in slight motion and the size of the projected image reduced by movement during the exposure, aiming to put a graduated fill into the graduated hole left in the first exposure.

More control can be had by using thin card masks either held on a below-lens filter holder, or on a sheet of plate glass forming a masking stage a little above halfway between lens and paper. I use a couple of piles of books on each side to support the glass sheet, enabling it to be raised or lowered by adding or removing a volume of suitable thickness, but others might prefer a more elegant solution. The supports rest on a board which also carries the enlarging easel, allowing the whole lot to be removed without disturbance from enlarger to enlarger.

Masks are made by putting the neg in the carrier, focusing on the baseboard, then putting card on the masking stage and pencilling round the projected area of the image where masking is which can then be cut out. Masks can be held in place on the glass with tape, or an adhesive putty.

The mask for the first exposure is carefully positioned, then the enlarging paper put in place and the first exposure made. The photographic paper is left in place, covered by a card to prevent fogging while the second mask is positioned,. using the first negative (use the red filter) as a guide. The whole setup is carefully moved to the second enlarger and aligned using the second neg (still keeping the paper covered and using the red filter). The second exposure can then be made.

An alternative and perhaps easier method is to make the first exposure and start developing the paper. As soon as the image becomes visible, rinse the print briefly with water and then wipe off surface moisture. The print is then positioned for the second exposure using the red filter. The paper is now less sensitive than normal and the second exposure will need to be several times as long as on dry paper - and the contrast may be noticeably lower. This method was taught me by a commercially successful UK photographer who used it for book jackets and magazine covers, but I find it too messy in my small darkroom.

For some purposes you can work even more simply - just printing the images on top of each other. In each area of the print the image with the least dense negative at that point will predominate. As so often in photography it depends on the effect you want, although here considerable experiment is likely to be called for. Since images build up on top of each other you will need to divide the exposure time between the images - and can experiment with different ratios. Interesting 'motion' effects can be made from a suitable single negative by moving the paper or enlarger head between or during exposures.

Similar logic applies to working in-camera with multiple exposures. Working against a black background will give little or no exposure to these areas, so you can take several pictures with no change from normal exposure so long the images don't overlap. However, where the film will get exposed in the same areas from each exposure you need to divide the normal exposure time between the exposures. In some of John Blakemore's large format landscape work from the 1970's the overall exposure of perhaps 2 seconds was divided into up to 50 short exposures, producing unique and exciting effects (some of his fine later work is on the web.)