The French photographer Louis Désiré Blanquart-Evrard introduced a variant of the salted paper print, known as the developed-out salted paper print. In a printed out salted paper print, a sensitized paper was left in the printing frame until the desired density was achieved. In a developed out salted paper print, the paper was exposed to light for a short time until the image began to appear. The image was made further visible through the use of gallic acid as a developer and then fixed. Developed out images had far greater light stability and very cool neutral tones (almost black). As developed out salted paper prints proved difficult to make, they did not appear to gain popularity among photographers.