Introduction to the
Wet-Plate Collodion Process
by Andrew Frith

This is a French 19th century Darlot lens. It is a Petzval lens design and is used wide open as the wet-plate emulsion is very slow (something in the order of 1 ASA). These old brass barrel lenses have little correction for distortions etc. that most modern lenses have and so they give a unique "victorian" look to portraits. The camera is a metal Calumet C-1 8x10 camera, which is a sturdy camera with a 6x6 inch lensboard which is convenient for mounting some of the heavier antique brass lenses.

POLISHING THE PLATE: A wooden vise is used to hold the black stained glass whilst scrupulously cleaning both sides with rottenstone, a mixture of whiting or calcium carbonate and alcohol. Once thoroughly clean a thin edge of albumen is applied around the sides of the glass. Once dried this thin albumen edging will help stop the collodion from peeling during the development stages.

PREPARING THE COLLODION: The collodion emulsion is a mixture of iodide salts (cadmium and potassium), ether, alcohol and collodion. After initially preparing the collodion, it is left to "ripen" for a week or so before use.

COATING THE PLATE: A puddle of collodion is poured onto the plate and then allowed to flow around the glass until an even covering is created. The excess is poured off into a separate container. Getting an even flow takes some practice as ridges can be formed if the solution is flowed back over itself during the coating process.

SENSITZING THE PLATE: Once coated the plate must be sensitized in a solution of silver nitrate immediately. A lidded vertical tank of plexiglass inside a wooden holder is often used. The plate is left in the silver nitrate solution for 3-4 mins. At this point the collodion emulsion takes on a creamy color. The back of the plate is then wiped clean of excess silver nitrate and inserted into a plate holder.

LOADING THE PLATE: A traditional wet-plate back is used or a modified modern film holder may be used. This wooden film holder has been modified to hold a full-plate size glass plate (6 ½" x 8 ½").

POSITIONING THE MODEL: The model must be positioned and set up prior to sensitizing the plate. Here a barely visible head-brace is being used to allow Mary Jo to keep her head in the same position.

NOTE: Mary Jo is the wife of Guild member Patrick Kolb and co-editor of the monthly Guild newsletter.

EXPOSING THE PLATE: A front-mounted Packard shutter is being used for the exposure. Exposure times with wet-plate range from several seconds to several minutes.

DEVELOPING THE PLATE: Once the exposure is made, the plate must be developed immediately. A small amount of a mixture of ferrous sulphate/acetic acid and alcohol is used and is flowed onto the plate in a similar manner to the collodion coating. Development times are as short as 15 seconds. At this point the image appears as a negative on the glass. Development is stopped by putting the plate under a flow of running water for several minutes.

FIXING THE PLATE: Fixing is done with either a strong mix of sodium thiosulphate or with potassium cyanide. During the fixing process the negative image fades away and then re-appears as a positive.

NOTE: Potassium cyanide should only be used by experienced practitioners and those with adequate chemical handling experience and equipment as mishandling of potassium cyanide may lead to cyanide gas being formed which is DEADLY!

WASHING THE PLATE: The plate should be thoroughly washed for at least 5 mins under running water.

VARNISHING AND DRYING THE PLATE: Finally the plate is varnished with a mixture of sandarac gum, lavender oil and alcohol. The plate is heated over an alcohol lamp and then the varnish is poured in the same way as the collodion emulsion. Once dry, the plate may be safely handled and is archival for several centuries at least.

If you have any questions about the wet plate process, please contact Andrew.

© 2006 by Andrew Frith (text) and Gerhard Bock (images). All rights reserved.