Should the gap however be too large for this, you will have to make a supplementary design to fill up the place. The same thing would be necessary in the case of your having to shorten a pattern.
To transpose and repeat patterns by means of looking-glasses (fig. [885]).—We have referred to the necessity that often occurs of adapting patterns to certain given proportions; this can in most cases be done easily enough without the help of a draughtsman, especially in the case of cross stitch embroideries, by means of two unframed looking-glasses (Penelope mirrors, as they are called) used in the following manner.
Fig. 885. To transpose and repeat a straight pattern by means of looking glasses.
If you want to utilize a piece only of a straight border, or after repeating it several times, to form a corner with it, you place the mirror in the first instance across it at right angles, at the place from which the pattern is to be repeated, and then exactly diagonally inwards.
To make a square out of a straight pattern, you take two mirrors and so place them that they touch at the point where the diagonal lines meet, as represented in fig. [885], and you have your square at once.
This is all easy enough, but before beginning any large piece of work it is necessary to consider carefully which parts of the drawing will best fill the centre and which are best suited to form the corners, as it is not every part of a straight pattern that is adapted for repetition.
A few preliminary trials with the help of the mirrors will better show the importance of these explanations than anything further we can say on the subject.
To alter the proportions of a pattern by dividing the ground into squares (figs. [886] and [887]).—Cases will occur where it will be found necessary to subject the pattern to greater modifications still than those we have hitherto been dealing with.