There is generally-accepted belief among photographers that a great amount of control can be exercised in development over the density and the general gradations of a negative, and in this respect alkaline pyrogallol enjoys a special reputation.
Photo-chemical Investigations and a New Method of Determination of the Sensitiveness of Photographic Plates (Reprinted from The Journal of the Society of Chemical Industry, 31st May, 1890, No. 5, Vol. IX)
[“The Photographic Research of Ferdinand Hurter & Vero C. Driffield” (A Facsimile Edition), Morgan & Morgan, Inc., Dobbs Ferry, New York 1974, p. 86]