When the horizon line is very crooked, and especially when light-coloured objects project far into the sky, it is necessary to use a mask. This is a piece of some opaque substance which may be placed between the landscape and the cloud negative so as to shade the landscape, the outline of the mask precisely correspond ing with the horizon line.
The best way to make a mask is to take a print as it comes from the frame untoned and unfixed, and to cut away the sky with a small pair of scissors. As it will be impossible to lay the print over the mask with ab solute precision it is best to cut away a very narrow strip of the landscape matter when making the mask. If the sky overlap the landscape by a thirty-second or even a sixteenth of an inch it will be unnoticeable, hut if there be the smallest white space left between the landscape and the clouds the effect will not only be noticeable but disagreeable.
When the mask is made it is applied to the sky negative which is to be used, the printed side of the mask being next the film side of the negative. The position of the mask with relation to the sky is altered till all the sky except what is to be printed into the picture is covered up. If several prints from the same negative are to have skies printed into them it is best to fix the mask to the sky negative with a couple of wafers or drops of gum at the lower corners. The print is now placed on to the sky negative, the adjustment between the two being made by looking through them from the negative side. Some patience is necessary to get the
horizon line to correspond precisely with the outline of the mask.
If it be desired to have the sky equally dark at top and bottom the frame is put out to print just as it is. It is usually best to have the sky somewhat darker at the top than at the bottom, and for this reason the shade is generally used for a part of the exposure.
When printing from paper or gelatine-film negatives a printing frame is not always necessary. The print may be laid on a board, over this the flexible negative, and above all two pieces of glass, one covering the lower part of the print, the other the upper, the line between them being an inch or so below the horizon. The shade or cloth is used over these precisely as over the frame, and when we wish to inspect the progress of printing all we have to do is to press firmly on the lower piece of glass so as to secure the print from movement, while we lift the upper glass and bend up the sky negative so as to examine the print which is below it.
As we have said, great judgment is necessary in determining how dark the sky is to be printed. The best effects are often got by skies printed very boldly, but great artistic skill is necessary in such a case. It is best in most cases to print very lightly. In any case the highest lights of the sky should be pure white, and the general tint of the sky should be lighter than the distant portion of the landscape.