In making corrections on brush drawings the parts to be corrected should be carefully washed out with a small short-cropped brush and water and still further cleaned by using a rubber eraser over an erasing shield or an opening cut in a piece of celluloid. Erasures should not be made on delicate work with a knife or a sand rubber, as either will injure the surface and affect reproduction. In measuring a specimen with dividers the draftsman should be careful not to injure the specimen or to puncture the paper on which he is preparing the drawing. PEN DRAWINGS. A draftsman who is preparing drawings of specimens with pen and ink should have a good assortment of pens equal to Gillott's Nos. 291, 290, and 170, liquid waterproof ink equal to that manufactured by Higgins, good pencils, hard and soft rubber erasures, plain dividers, and Reynolds's bristol board. A glass eraser is also useful. Good pen drawings of specimens are much more difficult to make than brush drawings. They can be prepared only by a draftsman who has had some artistic training and experience in pen work. Few draftsmen can prepare pen drawings that faithfully represent both the detail and the texture of specimens; the shading on many such drawings confuses and destroys both detail and texture. The pencil sketch over which a pen drawing of a specimen should be made must be prepared in much the same manner as the sketch for a brush drawing, though the outlines need not be so delicate. This sketch is generally made on bristol board. The pen work should begin with the outlines and should then be carried to the details, and finally to the shading, whether in lines or stipple. The texture of a specimen is the best key to the proper shading. If the specimen is decidedly granular, stippling is appropriate; if it is smooth or polished, finely drawn parallel lines, varied in spacing and character according to depth of shade and texture, are preferable. Erasures can be made with a hard-rubber eraser, other parts being protected by a shield, or with a very sharp knife or a glass eraser, and the parts erased can be resurfaced with an agate burnisher. RETOUCHING PHOTOGRAPHS OF SPECIMENS.