The shade of color I use is a light reddish-brown.

Tripoli, rotten-stone, or any earthy matter, may be applied in the same manner.
Transparent or Invisible Back-ground .-- I give this as originally published in my System of Photography, 1849: "Take a large woollen blanket with long nap, the longer and rougher it is the finer will be the effect produced; stretch it on a frame of sufficient size, and suspend the frame at the centre of the upper end by a string fastened to a nail in the ceiling, from three to five feet back of the sitter.

Having arranged this, fasten another string to the side of the frame, and while the operation is going on in the camera, swing the back-ground from right to left, continuing this during the whole time of sitting, and you have a clear "transparent" back-ground, which throws the image out in bold relief, and renders the surface of the plate invisible.

If equalled at all it is only by atmospheric back-ground.

I consider it to be the best ever known, and think it needs but to be tried to afford satisfactory proof that it is so.
Although used by few before, since the first edition of this work at least two thirds of the operators have adopted its use; for any one can at once understand the principle and the effect which it produces." It may be added that a motion imparted to to any back-ground where softness is desired, produces an excellent effect.
Gilding Dissolvent .-- To one quart of muriatic acid add as much oxide of iron (common iron rust) as it will dissolve in two days.