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Appendix 7: Photographic Processes

Postive Photographic Images

On Metal

A Image is on highly polished silver. Daguerreotype (1839-1860s)
B Dull image on black or brown varnished iron Ferrotype or Tintype (1852-1940s)
C Image is on copper, aluminium, zinc. May be sepia, black and white or colour. Carbon-transfer (1864-1930s) or Transferrotype (1884-1930s)
D Image is on white enamelled copper plate. Photo-ceramic (1860s on)

On Miscellaneous Bases

A Synthetic ivory Ivortype (1855-1910), Eburneum (1865-1910s)
B Fabrics - cotton, silk, linen Cloth print (1850 on)
C Fabrics, oil cloth Planotype (1854-1900) wet collodion positive
D Fired glaze image on china or porcelain Photo-ceramic (1860s on)
E Image on wood, stone Carbon transfer (1864-1930s) or Transferrotype (1884-1930’s)

On Glass

A Dull negative image made positive by viewing against a dark background. Collodion positive, also known as Ambrotype (1851-1870s)
B Positive image on opal glass. Opaltype (1880-1920)
C Print on convex glass, translucent, hand tinted. Crystolleum (1880s-1930s)
D Images on 3¼" x 3¼" to 3½" x 4" glass plates - can be collodion, gelatin carbon, dyed or hand-tinted. Lantern slides (1851-1900)

Identification of Prints

(10 x – 30 x magnification)

Single Layer Paper Support

A Uncoated single layer paper. Paper fibres clearly visible with the image formed in the paper fibres. Purple to warm sepia highlights, yellow especially at the edges. Salted paper print (1840-1860s)
    Neutral grey or brown image, no fading. Platinotype (1880-1920s)
    Bright blue image. Cyanotype (1840s) Negative image
Cyanotype (1880-1920) Positive image
    Shows regular pattern. Photomechanical process (1870-on)

Double Layer Paper Support

B Double layer paper, fibres may be visible through the binder layer. Purple to red brown image. Usually yellow in the highlights, cracking of binder layer. Albumen print (1850-1920s)
  Paper fibres visible. No image fading. Can be any colour. Woodburytype is normally chocolate brown with distinct image relief. Carbon print (1860-1900s) Pigment print
Woodburytype (1865-1890s)

Triple Layer Paper Support

C1 Fibres visible. Water spot test shows swelling. Warm purple to red brown image. Gelatin printing out paper (1880-1920)
  Paper fibres invisible. Water spot test shows swelling. Silver mirroring may be seen in high density areas. Gelatin developing out paper (1880-on)
C2 Paper fibres invisible. Water spot test has no effect.   Collodion printing out paper (1880-1920)
  Water spot test has no effect. No image fading. Neutral image hue. Matt collodion printing out paper with gold and platinum toning (1880-1920s)

Negative Images

On Paper

A Plain uncoated writing paper Calotype (1840-1860s)
  Translucent waxed paper Calotype (1851-1865) Waxed paper negative
  Oiled paper Eastman negative paper (1884-1895)

On Glass

B Image often creamy Wet collodion (1851-1880s)
    Dry collodion (1854-1885)
    Albumen (1848-1920s)
  Image is black and may be tarnished. Gelatin dry plate (1880-on)

It is difficult to differentiate between wet collodion, dry collodion and albumen images. An alcohol spot test which dissolves the collodion may be necessary

On Film

C There are no easily discernible visual differences between these film types Cellulose nitrate (1889-1950)
    Cellulose acetate and tri-acetate (1930-1960s)
    Polyester (1965-on)

These film types can be identified by putting a small sample in a test tube containing trichloroethylene. During a 10-second time test, the cellulose nitrate sinks to the bottom, the acetate hovers about the middle and the polyester floats to the top.

Alternatively, a small sample (pin-head size) can be examined by infra-red spectroscopy. This specialised and somewhat expensive technique will allow unambiguous identification.