For red-writing fluids for blueprints, take a piece of common washing soda the size of an ordinary bean, and dissolve it in 4 tablespoonfuls of ordinary red-writing ink, to make a red fluid. To keep it from spreading too much, use a fine pen to apply it with, and write fast so as not to allow too much of the fluid to get on the paper, for it will continue eating until it is dry.


For red and white solutions for writing on blueprints, dissolve a crystal of oxalate of potash about the size of a pea in an ink-bottle full of water. This will give white lines on blueprints; other potash solutions are yellowish. If this shows a tendency to run, owing to too great strength, add more water and thicken slightly with 'mucilage. Mix this with red or any other colored ink about half and half, and writing may be done on the blueprints in colors corresponding to the inks used.


Add to a small bottle of water enough washing soda to make a clear white line, then add enough gum arabic to it to prevent spreading and making ragged lines. To make red lines dip the pen in red ink and then add a little of the solution by means of the quill.


For white ink, grind zinc oxide fine on marble and incorporate with it a mucilage made with gum tragacanth. Thin a little for use. Add a little oil of cloves to prevent mold, and shake from time to time.


A fluid which is as good as any for writing white on blueprints is made of equal parts of sal soda and water.


Mix equal parts of borax and water.

Both these fluids, V and VI, must be used with a fine-pointed pen; a pen with a blunt point will not work well.