Emulsion Transfer with Glass Negatives

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Conservation Treatments


To transfer the emulsion to a new base is a very drastic and risky treatment and should only be considered if there’s no other possibility to preserve the image.

In every case all negatives treated in this way should be duplicated first.

The recommended techniques can also be carried out if the emulsion is already flaked off.

Gelatin Glass Plates

1. The new glass base has to be prepared as follows:

  • Cleaning, e.g. bath of chromic sulphuric acid for 18 hours (70g potassium chromate, 70g concentrated sulphuric acid, 1l distilled water), subsequent rinsing
  • Neutralization by a solution of sodium carbonate (5% in water), subsequent rinsing
  • Application of a substratum, different formulas:
    • Application of two layers of gelatin solution (1. 5g gelatin, 0,5g chrome alum, 5ml photo-flo (1:200 in water), 500ml water; 2. 4g gelatin, 100ml water; water should be warmed up to 45-50°C)
    • Bath of 20% gelatin and 1% potassium chromate in water, then application of 4% gelatin in water by a pipette
    • Application of a solution of 1% sodium silicate in water by a pipette
    • Application of a solution of 1% gelatin and 0,1% chrome alum in water
    • Application of a solution of 1g gelatin and 6ml solution of chrome alum (1:10) in 300ml water[1]
    • Application of a gelatin solution containing 20g gelatin, 5ml glycerol, 20ml water, 20ml solution of chrome alum (1:10)[2]
    • Application of a solution of albumen[3]
  • Vertical drying

2. Hardening of the gelatin emulsion to prevent swelling, different formulas:

  • Bath of 2% formalin for 3 minutes (20ml formalin (37-40%), 5g anhydrous sodium carbonate, 1l water): hardening lets protection varnishes become hazy which should be removed before hardening
  • Vapors of formaldehyde[4]

3. Separation of the emulsion, different formulas:

  • Bath of 1% hydrofluoric acid for 30 seconds (50g sodium fluoride, 10ml concentrated sulphuric acid, 1l water)
  • Bath of 4% hydrofluoric acid in water[5]
  • Place the glass plate negative emulsion side down onto a Vaseline coated glass plate, then bath in a solution of 0.5% sodium fluoride, 1% concentrated sulphuric acid in water (the transfer to the new base follows directly). If the old glass base is broken, the pieces can be temporarily adhered to each other by filling the gaps with a solution on 3% gelatin in water.


Separation of the emulsion by using hydrofluoric acid is possible since the hydrofluoric acid dissolves glass by formation of silicon fluoride (thus the use of trays of glass or porcelain is not recommended).

The less the concentration of hydrofluoric acid the longer the time required for separation. Since hydrofluoric acid is quite toxic alternatively a bath of a solution of sodium or potassium fluoride, with subsequent bath of diluted acid can be used. Then the hydrofluoric acid is built directly in the gelatin emulsion.[6]

  • Contrast bathes for some minutes (alkaline/ acidic): e.g. solution of sodium carbonate (1:500 in water), subsequent solution of hydrochloric acid (1:500 in water): separation by formation of carbonic acid[7]
  • Incising of the emulsion along the edges, then bath of 50-55°C warm water, emulsion can be separated be using a small brush.[8]


4. Neutralization of the emulsion: at least 3 sequenced bathes of water 5. Transfer of the emulsion (best carried out in water bath), different methods:

  • Let emulsion lie upside down onto a temporary base like polyester mat
  • Transfer to new, prepared, humidified glass plate


Combinations of steps 2 and 3

  • Bath of formaline and glycerol for 30 minutes (2ml saturated solution of potassium carbonate, 1ml glycerol, 1ml formaline, 50ml water)
  • Bath of sodium or potassium carbonate solution (5g in 100ml water, additional 15-20ml formaline replaces hardening step), after drying emulsion can be peeled off[9]

The swelling of the gelatin in aqueous bathes barely can be avoided, thus if the emulsion is cracked most probably there will be gaps in the dried emulsion on the new base.[10]

Collodion Glass Plates

The only formula found to transfer collodion emulsion is a historical one:[11]

  1. An interlayer of natural rubber, gutta-percha, gum arabic or gelatin is applied on top of the collodion layer
  2. A collodion layer is following consisting of collodion in ether and alcohol (addition of a plasticizer like castor oil is possible), alternatively a piece of paper or gelatin foil can squeezed on
  3. Then the whole package can be peeled off


References

GILLET et al., 1986

  1. ? STENGER, ERICH, 1909/10, p 132
  2. ? STENGER, ERICH, 1909/10, p 132
  3. ? STENGER, ERICH, 1909/10, p 132
  4. ? POLLMEIER, KLAUS, 1995
  5. ? POLLMEIER, KLAUS, 1995
  6. ? STENGER, ERICH, 1909/10, p 115 et seq., 132
  7. ? STENGER, ERICH, 1909/10, p 133
  8. ? STENGER, ERICH, 1909/10, p 150
  9. ? STENGER, ERICH, 1909/10, p 149
  10. ? POLLMEIER, KLAUS, 1995
  11. ? STENGER, ERICH, 1909/10, p 102
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