This section is from the book "Modern Photography In Theory And Practice", by By Henry G. Abbott. Also available from Amazon: Modern photography in theory and practice: A hand book for the amateur.
We will now consider the method of making bromide enlargements at night, using an inexpensive, home-made contrivance, not very handsome but fully as capable of good results as the best enlarging apparatus. Procure a good, sound box, say 14 inches square and another smaller box, say 10 inches square. Remove the cover from the large box and cleating it together put on two small hinges, so it will act as a door for this box. In about the center of the bottom a pair of condensing lenses should be fastened. These lenses are used to distribute the light evenly all over the negative, otherwise you would have a bright spot in the middle, with a gradual diminution of light towards the edges. Cut the second, or smaller box, down to say 10 x 10 x 3 and cut a hole in the bottom of this a little smaller than your negative. On the outside of this fasten three strips, with thumb tacks projecting over the edge for the reception of your negatives, as described when making enlargements by daylight, or grooved pieces can be used and the negative slide in the grooves. This smaller box should be fastened to the larger one so that the negative will come opposite the center of the condensing lenses and about three inches from them. Procure an elbow of speaking tube, about four inches long and cut a hole in the top of the large box so this tube will fit into it friction tight. Turn the opening of the tube towards the door in the box. In the box place a gas stand with a Welsbach burner, or what is better if you have it, an acetylene gas bicycle lamp. Any good oil bicycle lamp will answer but the purer and stronger the light the shorter the exposure will be. The flame of the lamp should be in line with the center of the condensing lenses. Remove the ground glass from your camera and back the camera up to the small box holding the negative.
Prop up the camera on a small box so that the opening which was occupied by the condensing lenses will be exactly opposite the negative. Make two wooden triangles and screw them to the back of a drawing board, to hold it in a vertical position, as explained when making enlargements by daylight. Make everything light-tight by pasting red express paper over any cracks in the boxes, or where the two boxes join one another. Throw the focusing cloth over the joint between the camera and box, to shut in any light which might escape. When all is ready, light the lamp and proceed to focus on a piece of white paper on the drawing board, as previously explained. Fig. 54 may help the amateur to understand more readily the above description. Enlarging by means of artificial light is more reliable than by daylight, for the source of light, as a usual thing, is constant, while with nature the light varies considerably every few minutes, owing to passing clouds.
Should we wish to enlarge say a 4 x 5 negative to 8 x 10 in size and leave a white margin around the print, we can readily do so by pasting a strip of black paper all around our 4 x 5 negative on the glass side, or we can do so by cutting a mask and placing it over the bromide paper when we get it in position. We can also vignette very nicely on bromide paper by taking a large sheet of cardboard, cutting a hole of the right size and shape in the center and moving it back and forth between the lens and the image on the bromide paper. A little thought will show you that the nearer you bring this vignetter to the bromide paper the smaller the circle of light and the closer you bring it to the lens the larger the circle of light which will fall on the paper. It is evident, therefore, that to vignette softly from the center to the edges that the screen or vignetter must be kept constantly in motion from the lens to the paper during the entire exposure. To get good, soft effects it will be found better to stop down the lens pretty well so as to prolong the exposure somewhat, say f 32. Cut masks of various shapes may be purchased from most of the large photo supply houses and these may be employed successfully by placing them over the negative when making bromide enlargements. The development, fixing and washing is the same as for bromide prints made by contact, as described on pages 145 and 146 but enlargements should be placed in a tray of clear water for a few minutes prior to development. The mounting can be done on a card, or on a piece of linen which has previously been mounted on a stretcher. If a white margin is left around the enlargement, a line, about a quarter or half inch from the edge of the print, drawn with a ruling pen and India ink, will enhance its general appearance and make it equal, when framed, to the finest steel or copper plate engraving.
Once the amateur has familiarized himself with the process of enlarging on bromide paper and sees the beautiful results that may be secured in so simple and inexpensive a manner, he may wish to own something better than the crude camera of home-made construction. In this event we should advise the purchase of an Anthony Enlarging Lantern. It is very simple in construction and is capable of making the very best styles of enlargements. It may also be used as a copying camera for making lantern slides. The grooves in the interior admit of changing the relative positions of the negative and the condensing lenses and it occupies a space of only 8 x 15 x 18 inches.