DEGRADATION OF GLASS NEGATIVES

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Degradation

Contents

[edit] Flaws related to original processing

  • flaws in the protection varnish of mostly collodion glass plates: milky appearance due to condensation, netlike breaks due to an overwarmed plate during application, reticulated surface due to too fast drying of the varnish, air bubbles

most of these flaws won’t be found in plates that are still existing since a defective varnish would have been removed directly after completion and replaced by a new one[1]

  • flaking off or breaks in the emulsion due to too much alcohol in the collodion solution or a insufficiently cleaned glass surface

(NORRIS, DEBBIE HESS, 1989d)

too much ether in the collodion solution lets the collodion dry too fast and shrinks, too much alcohol makes the collodion layer thin and brittle

(GILLET et al., 1986)

sometimes these flaws were over-varnished or retouched

(McCABE, CONSTANCE, 1991)

[edit] Deterioration of the glass base

  • glass corrosion
  • breakage of glass due to mechanical stress or micro-cracks formed by ongoing glass corrosion

(BARGER, 1985)

  • deformation of the glass (Gelatin Dry Plates)

(ADELSTEIN et al., 1977; EASTMAN KODAK COMPANY, 1973)

since gelatin is very hygroscope and glass not, extreme fluctuations in the surrounding humidity will result in strong tensions between glass and emulsion. These tensions can lead to a deformation or bending of the glass by the due to dry climate contracting gelatine. This happens especially with plates of bigger formats (careful not to break them during contact printing)

(McCABE, CONSTANCE, 1991)

[edit] Deterioration of the emulsion

  • Collodion emulsions mostly in quite good condition due to high quality protection varnishes, most changes are related to deterioration of the base material glass

(McCABE, CONSTANCE, 1991)

  • Hydrolysis of collodion emulsion noticeable in yellowing, softening and stickiness (which can lead to several glass plate negatives sticking to each other) mostly due to the influence of alkaline glass corrosion products (like sodium hydroxide, sodium silicates). This process can be accelerated by the presence of a protection varnish since the decomposition gases from the emulsion can’t escape

(GILLET et al., 1986; McCABE, CONSTANCE, 1991)

  • Abrasion (especially with areas of collodion negatives which are not varnished[2]
  • flaking off sometimes due to the glass corrosion products which makes the glass-emulsion-interface porous.

(McCORMICK- GOODHART, MARK H., 1992a; McCABE, CONSTANCE, 1991)

In Gelatin glass plates tensions between glass and gelatin due to extreme changes in humidity can lead to flaking off of emulsion.

(GILLET et al., 1986; WAGNER, SARAH, 1989)

Sometimes the adhesion between glass and gelatin is that strong that pieces of the glass are torn off when the gelatin contracts.

(McCABE, CONSTANCE, 1991)

Further causes for flaking off can be a cutting edge, extensive hardening of the emulsion and a very thick emulsion layer.

(PROTZE, SABINE, 2002)

Also the degradation of the substratum can be a reason for flaking off.

(VIARS, DOMINIQUE, 2001; REMPEL, SIEGFRIED, 1987, p 93 et seq.)

A survey did show a white covering on many glass plates where the emulsion was flaking off which was analyzed not to be related to the glass corrosion products and so was reasoned to be connected to the substratum.

(VIARS, DOMINIQUE, 2002)

[edit] Deterioration of coatings

  • Hydrolysis of the protection varnish noticeable in yellowing, softening and stickiness (increases with increasing surrounding humidity ) mostly due to the influence of alkaline glass corrosion products (like sodium hydroxide, sodium silicates)

(McCORMICK- GOODHART, MARK H., 1992b; McCABE, CONSTANCE, 1991; McCORMICK- GOODHART, MARK H., 1992a)

  • Yellowing and brittleness with resin-based varnishes

( PEDERSEN et al., 2005)

  • Nearly all resins tend to oxidation fastened by light: mastic and sandarac are bleached, other resins darken

(HANSCH, MARTIN, 1985, p 63)

[edit] References

  1. ? PEDERSEN et al., 2005. Pedersen, Karen Brynjolf; Kejser, Ulla Bøgvad; Johnsen, Jesper Stub; Christensen, Mads Chr.. Coatings on Black-and-white Glass Plates and Early Film. In: Constance McCabe ed. Coatings on Photographs. Washington D.C.: AIC. 108-131
  2. ? PEDERSEN et al., 2005. Pedersen, Karen Brynjolf; Kejser, Ulla Bøgvad; Johnsen, Jesper Stub; Christensen, Mads Chr.. Coatings on Black-and-white Glass Plates and Early Film. In: Constance McCabe ed. Coatings on Photographs. Washington D.C.: AIC. 108-131
  • ADELSTEIN et al., 1977. Adelstein, P.Z.; Gray, G.G.; Burnham, J.M.. Manufacture and physical properties of film, paper and plates. In: John M. Sturge ed. Neblette's Handbook of Photography and Reprography. Materials, Processes and Systems. New York: Van Nostrand Reinhold Company, 127-147
  • BARGER, 1985. Characterization of Deterioration of Glass Supported Photographic Images. In: Second international Symposium: The Stability and Preservation of Images (Advanced Printing of Paper Summaries), 25.-28.08.1985, Ottawa, Canada, 17-20
  • EASTMAN KODAK COMPANY, 1973. Physical Characteristics of Glass for Kodak Photographic Plates. Rochester, NY: Eastman Kodak Company (Kodak Publication No. Q-35)
  • GILLET et al., 1986. Gillet, Martine; Garnier, Chantal; Flieder, Francoise. Glass Plate Negatives. Preservation and Restoration. Restaurator, 7(2), 49-80
  • HANSCH, MARTIN, 1985. Frühe Photographien - ihre Technik und Restaurierung. Überherrn/Saar: Kabinett-Verlag Uwe Scheid
  • McCABE, CONSTANCE, 1991. Glass Plate Negatives: The Importance of Relative Humidity in Storage. In: Sauvegarde et Conservation des Photographies, Dessins, Imprimés et Manuscrits. Actes des Journées Internationales d´Études de l´Arsag, 30 sept.-4 oct. 1991, Paris. Paris: Association pour la Recherche Scientifique sur les Arts Graphiques, 36-44
  • McCORMICK- GOODHART, MARK H., 1992a. Glass Corrosion and its Relation to Image Deterioration in Collodion Wet- Plate Negatives. In: The Imperfect Image; Photographs their Past, Present and Future, 6th -10th April 1992, Windermere, 256-265
  • McCORMICK- GOODHART, MARK H., 1992b. An Analysis of Image Deterioration in Wet- Plate Negatives from the Mathew Brady Studios. In: The Imperfect Image; Photographs their Past, Present and Future, 6th -10th April 1992, Windermere, 256-265
  • NORRIS, DEBBIE HESS, 1989d. Ambrotype. University of Delaware
  • PEDERSEN et al., 2005. Pedersen, Karen Brynjolf; Kejser, Ulla Bøgvad; Johnsen, Jesper Stub; Christensen, Mads Chr.. Coatings on Black-and-white Glass Plates and Early Film. In: Constance McCabe ed. Coatings on Photographs. Washington D.C.: AIC. 108-131
  • PROTZE, SABINE, 2002. Festigungsmittel zur Sicherung sich lösender Emulsion. Rundbrief Fotografie, 9 (3), 12-15
  • REMPEL, SIEGFRIED, 1987. The Care of Photographs. New York: The Lyons Press
  • VIARS, DOMINIQUE, 2001. Diplomarbeiten 2001: Gelatinetrockenplatten. Rundbrief Fotografie, 9 (2), 14-15
  • VIARS, DOMINIQUE, 2002. Analyse et conservation- restauration des négatifs au gélatino- bromure d'argent: vernis sur plaque de verre prédentant un soulèvement de l'image. Support tracé, 2, 33-39
  • WAGNER, SARAH S., 1989. A Preliminary Study: Consolidation of Gelatin Glass Plate Negatives with Organosilanes. Topics in Photographic Preservation, 3, 69
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