Examples from the Web for restrainer
The development is extremely slow, without any tendency to fog; thus the addition of a restrainer should be avoided.
The bromide is called a restrainer, as it makes the development of the image proceed more slowly.
He was best known for his tannin process and alkaline developer, with a bromide solution as a restrainer.The Evolution of Photography |John Werge
The restrainer has been withdrawn, and the beast has stepped forth in the plenitude of his power.The Expositor's Bible: The Book of Revelation|William Milligan
The negative must be carefully developed, using plenty of restrainer.Photographic Amusements, Ninth Edition|Walter E. Woodbury and Frank R. Fraprie