One of the most common details in the routine of the drawing-office is the mounting and repairing of tracings and drawings which have either been made on paper too flimsy to stand the wear and tear which they will have to undergo, or which are falling to pieces from the rough treatment which they have received in the shops or elsewhere. Like many other minor details, it often fails to receive the attention which, if paid to it, would be amply repaid. It is usually the first task assigned to a new pupil, who, from ignorance of the materials used, and of the best method of setting about his work, too often "makes a mess of it." To avoid this, and to save the time which it occupies, it is a very common practice to use "tracing-cloth " for all tracings which are likely to be frequently handled and folded. Every one knows the disagreeable nature of this material. From its "greasiness," as compared with ordinary tracing-paper, a "greasiness" which cannot be overcome by ox-gall, it is difficult to make the ink "lie," and, from its non-absorbent qualities, the lines take much longer to dry and are more liable to be smeared.
As the ink lies on the surface, the lines are liable to wash, and any colouring that may be necessary has to be applied en the back or wrong side, and any erasure that may be necessary, or any accidental drop of water, leaves a disagreeable white mark. It is no exaggeration to say that three tracings may be made on ordinary tracing-paper in the time required to make two on tracing-cloth. The method which we are about to describe is not only satisfactory, but very easy, and requires only ordinary care, and no special skill.
Let us suppose that we wish to mount a tracing. We take a drawing board, which must be perfectly clean and made without glue in the joints, and lay it on a table, or on trestles, if possible, so that we can get at. it from all aides. We then take a stout piece of calico, about an inch larger all round than*the tracing to be mounted, and pin it down with a tack at each corner on another table, which we have previously covered with old newspapers. We then lay the tracing face downwards on the drawing-board, and with a soft sponge wet it thoroughly all over. Then, raising first one half of the tracing and then the other, we flood the board well with clean water. The tracing now lies floating on a thin film of water. Then, taking a moist sponge and commencing at the centre, and working outwards towards the sides in turn, we press the tracing down on to the board, driving the water out at the edges. In the same manner we work out all the water from each corner in turn, always working from the centre to the edges, and taking care to leave no *' blobs " of air or water behind us, and wiping off all superfluous moisture from the top or back of the tracing. By viewing it slantwise across the light, it is easy to see if this has been properly done.
If it is an old or badly-torn tracing, we can easily fit any detached pieces and, as it were, glue them down in their place on the board with the water. If it is necessary to unite two sheets, we first lay down the larger, if of different size, as above described, and then the other, commencing from the point of junction and working outwards. Then, with a stout brush we spread the paste - which we suppose already prepared - well, and evenly over the calico, beating it thoroughly into the interstices of the cloth and taking care to leave no lumps or superfluous quantity, and, if necessary, picking off any bristles out of the brush, etc. Then, taking it by the corners (this is the only part of the operation in which any assistance is required) and turning it over and holding it at full stretch, we lay it on the tracing, taking care that, as far as possible, every part shall come in contact at the same moment. Once down it must not again be lifted, or it will probably pick up any loose pieces and remove them from their proper positions. Then, with the wet sponge, we proceed to press down the cloth in the same manner as we have previously spread the tracing, driving all air-babbles out at the edges and wiping off all superfluous moisture.
Then, turning back each corner in succession, as at B1, till we can just see the corners of the tracing, we stick in four tacks or drawing-pins, not to hold it down, but merely to mark the corners. A A (Fig. 16) is the board;
B B, the cloth; B1, one of the corners turned back; C C, the tracing underneath; C1, C1, tacks at the corners. Then, pressing the corners down again, we set aside to dry. If wanted in a hurry, it may be dried, not too quickly, before the fire, allowing at least two hours for this process; but it is better to allow it to dry slowly and leave it until the next day. When dry, cut with a sharp knife from tack to tack, and the tracing will fall off. If the paste is good, it will be easier to split the paper than to tear it off the cloth. The remaining strips of cloth may then be torn off the board, and the board washed free from all traces of paste for future use.
It might be supposed that the colouring would run, and the lines be found all blotted and blurred after such rough usage, but such is not the case. Indian yellow, if laid on too thickly, will occasionally run, but not to a serious extent, and heavy lines of Prussian blue would probably be found printed and reproduced on the board, but not blurred or smeared. But the best plan, if a very neat appearance is a sine qua non, is to colour the tracing after mounting. The tracing will be found to have a surface for colouring far superior to the best drawing-paper, and as all superfluous ink has been removed by the process, lines and figures may be washed over in the most careless manner without any fear that they will run. Those who know the care required to wash over a heavy dotted line, will fully appreciate the advantage.
The absence of all distortion is a most remarkable feature in tracings mounted as above described, and may be readily tested by applying a straight-edge to any line. Any expansion or contraction is equal in all directions, and may be almost entirely obviated by a careful adaptation of materials. Very thin tracings should not be mounted on very thick cloth, or vice versa. It will also be found that some tracing-papers will expand very much more than others, and, as is well known, will, if left free, contract upon drying to less than their former dimensions. But this tendency is counteracted, not only by the fact that the tracing remains stretched on the board until dry and cut off, but by the fact that the cloth will not contract upon drying, especially if the paste is well beaten into the interstices.
So far we have described the process as applied to thin tracings, but it is equally applicable to torn drawings upon thick paper and to drawings made on the commoner sorts of drawing-paper when it is not thought worth while to employ the superior qualities which are sold ready mounted on cloth. By soaking old and valueless drawings and tracings in water for a few hours, the cloth may easily be peeled off and used again. If it is desirable to leave a margin wider than that on the unmounted tracing, the cloth may be detached from the board where it adheres at the edges by using an ivory paper-cutter or a feather-edged scale. If small parts of the tracing have been torn out and lost, the cloth will, of course, adhere to the board at these points, and must be carefully detached in the same manner. If desired, stout paper may be used instead of the cloth, though not so good or so easily applied. Of course, white calico must be used, as unbleached cloth shows an unsightly colour through the tracing. If any corrections or erasures should be necessary, we recommend the following plan: - To take out a line, fill a drawing-pen with clean water, and, setting it at a rather coarser pitch than the original line, rule over the line.
Let the water lie for a few moments, then dry with blotting-paper, and rub out with soft rubber. By repeating the process once or twice, the line will be perfectly erased. The surface may then be polished with the ivory paper-cutter or with the blade of a knife. To take out a blot or a shade of colour, use a wet brush instead of the drawing-pen. An obstinate blot may be removed by scratching it out with the point of a drawing-pen dipped in clean water, blotting the water off the tracing as often as it gets discoloured. This proceeding, however, will not improve the drawing-pen.
We will next suppose that it is desired to mount a plan or a map (such as a quarter-sheet, of the Ordnance Survey) in sections, so as to fold for the pocket or for insertion into a book. These maps usually have a very liberal margin, which, as so much waste paper, is better cut off, Raving decided on the final size, prick the corners through, as at aaaa (Fig. 16). Turn it face downwards, and rule lines all round from prick to prick. Then mark it off into the requisite number of squares, which must, of course, be of exactly equal size. Then number the squares in succession before cutting. If this is not done, some comical results will often occur through the sections being mounted in wrong sequence. Then cut it up. It is as well to leave a slight margin, as shown by the dotted lines at b b b b, so as to allow the edges to be finally trimmed up with a sharp knife. Then with a blacklead pencil rule two or more lines on the drawing-board at right angles to each other, as cc, dd (Fig. 16). Then, having soaked each square for about half a minute, lay them one by one on the wetted board, commencing with the centre sections 2, 3, 6, 7, and leaving about 1/8 in. between each section. When these have been properly placed and stuck down, the others, as 4, will follow.
Then apply the pasted cloth as above directed. In removing a map thus mounted in sections from the board, it will be found that in the narrow spaces between the sections it will probably adhere to the board, and the paper-cutter must be used to detach it, care being taken not to "start" the edges, and especially the corners, of each section with the edge of the cutter. If the map is to be attached to a book or case, a margin of cloth must be left on that section which is to be attached. When removed from the board, fold it carefully in the manner which appears most handy (in the above instance, first along the line cc, and then along the other lines backwards and forwards alternately), and press it for a short time under a heavy weight. It will afterwards naturally and without difficulty fold in the same manner. In the case of a larger map with three or four rows of sections, first fold all the horizontal and then all the vertical lines, or vice versa, and always in a zigzag form, alternately in and out. The above process, though rather complicated to describe upon paper, is remarkably easy to put in practice. There is, however, one class of drawings, or rather engravings, to which it is not applicable.
We allude to those upon unsized paper, such as is employed for the French Government maps, and for some lithographs. This when wetted, becomes as tender as wet bio ting-paper, and is very difficult to handle. We have sometimes employed the following process: - Having arranged the sections, dry or only slightly damped, on the board, we strain the cloth, which must be of an open texture, tightly above them, and then apply glue, as hot and liquid as possible, to the back. This, penetrating the cloth, will produce the required adhesion.