In search of the ideal formula

1.  INDEX
1.  Introduction
2.  Turnbull blue, Prussian blue and the Cyanoptype
3.  The Ammonium Iron Citrate
4.  The Formulae
5.  The Variables
6.  Recipes from the Members
7.  Conclusions
8.  Bibliography




1.  Introduction 
This article was born from the wish to put order in some of my notes on cyanotype, but it demonstrated that a so simple and old process (note 1) may be the object of consideration way far from the simple application of a phogographic recipe, becoming an example of a methodological approach with which analyze also other more complicated processes.

Some time ago, preparing the article on the cyanotype reportet in our "recipes" pages, I looked in the Web and in some othe publications the confirmation of my knowledge and eventual new tricks, suggestion and other.

It soon emerged that, in addition to the suggestions on how-to prepare the paper, the coating and the washing, many recipes were found for the sensitizing solution. Sure, this is not a new, (see for an example the kallitype and related processes), but I have never seen a so large number for a single process, and moreover I have never found comparisons justifying these differences, with the exception of one case.
Limiting myself to the most simple formula (the same reported in "recipes"), I have found as many as 25 variants, while considering also the presence of oxalic acid or other components this number almost doubles. Some variants are probably due to rough approximations converting from British to Metric units, nevertheless their number remains inexplicably high.

Who wish to go deep into this argument may read the Mike Ware's book "Cyanotypes" (Ware 1999), or -about the historical and aesthetical aspects- the thesis of Malin Hylen for a Graphic Art School published in the Web (Hylen 2000), while I report here only my personal notes, extracted from different sources.


2.  Turnbull blue, Prussian blue and the Cyanoptype 
The sensitizing solution for the cyanotype is as simple as disarming: it is sufficient to mix with water some ammonium iron citrate and potassuium ferricyanide. That's all. By means of the UV light, some of the trivalent iron turns to divalent, forming the ferrous ferricyanide Fe3[Fe(CN)6]2 (Turnbull blue), insoluble and highly coloured. The Turnbull blue is similar to the Prussian blue (ferric ferrocyanide, Fe4[Fe(CN)6]3), one among the first blue pigment sintetized at the begining of the XVIII century (note 2). 
It has been ipothesized that the two blue, the Turnbull and Prussian ones, are the same substance (Kleinke 2001): at the moment of the reaction, the divalent and trivalent iron atoms may exchange to give a unique product, where the Fe(III) is bonded to the carbon of the cyanide group CN, and Fe(II) is bonded to the nitrogen in a crystalline lattice with an octahedral structure (note 3). This may happen because the Fe(III)-cyanide complex is more stable compared to the Fe(II) one (Scheimreif 2000): 


  K+ + Fe3+ + [FeII(CN)6]4-  --> KFeIII[FeII(CN)6]    intermediate for the Prussian blue

  K+ + Fe2+ + [FeIII(CN)6]3-  --> KFeII[FeIII(CN)6]    intermediate for the Turnbull blue

The reaction leading to the cyanotype is possible because of the presence of citrate, which counterbalances the reduction from Fe (III) to Fe (II) oxidizing itself to CO2, that of ammonium ion, which stabilizes the iron complex (Abrahamson 1999), and the insolubility of the Turnbull blue removing the divalent iron. Furthermore, it has been found that the photochemical reaction has its maximum yield in a pH range between 2 and 5. It must pointed out that these measurements were done in solution, while in the cyanotype the mixture on the paper is almost dry.

To complicate all this things, also the reduction of ferricyanide to ferrocyanide, which can form the ferric ferrocyanide (Prussian Blue) combining with the excess of iron(III) citrate. If the ferrous ferricyanide which is part of the yet formed image is reduced, it will turn into the whitish ferrous ferrocyanide. This preferentially happens in the most exposed zones, and this reaction is responsible of the partially solarized aspect which usually indicates when to stop the exposition. The ferrous ferrocyanide will be oxidized again to ferric ferrocyanide with time and with the air exposition of the print, or it can be almost istantaneously oxidized adding some hydrogen peroxide to the last washing. Also the hydrochloric acid behaves in the same way, but this time it is because the oxidative reaction needs some acidity for speedly going on .


3.  The Ammonium Iron Citrate
The iron compound now used, the ammonium iron citrate green, is known "only" since 1898 (Seigel 2000a): before that year the brown form was used, and it was about 8 times less sensible than the green one. It is commonly referred to as a "ill-defined" compound, even if Clerc (Clerc 1950) gives the chemical formula for both the two forms: the green one corresponds to two molecules of ferric citrate plus one of ammonium citrate (m.w. 733.14), while the brown one is less easily interpretable and its molecular weight would be 615.04.
The iron citrate manufacturer declare an iron amount of 14.5-16% in the green form (the theoretical value is 15.2%), and 16.5-18.5% in the brown one (the theoretical value, assuming the Clerc's formula were true, is 18.16%).

On the basis of these information, the stoichiometric balance of the reaction between the green citrate and the potassium ferricyanide (in presence of the light) forming the Turnbull blue (Fe3[Fe(CN)6]2) needs a ratio of 1:0.6 by weight for the green form and 1:0.72 for the brown one (as an example, 10g of green citrate and 6g of ferricyanide). Taking into account also the reduction of the ferricyanide, the ratio rises only a few (1:0.64 for the green form). Instead, if one points to the formation of KFe[Fe(CN)6] (see the previous paragraph), then the ratio becomes about 1:0.9.
Some consideration of chemical nature would suggest to increase the amount of ferricyanide compared with the stoichiometric ratio, in order to favour the reaction. Instead, as it will be seen below, in the practice of the cyanotype the ratio between the green citrate and the ferricyanide is usually held slightly lower, about 1:0.5.

Finally a practical remark: the solution of ammonium iron citrate tends, still after a few days, to form a mould in its surface. To preserve it you can add some antifermentative (i.e. thymol, salycilic acid) or, as suggested by Clerc, to let a little bit of camphora floating over its surface.


4.  The Formulae
Limiting the formulae to those with the green form, and calculating all the amounts for 100 ml solutions, the "historical" texts give these recipes:

Namias (1929)
Sol. A
Ammonium Iron Citrate green 24 g
Water to make 100 ml
Sol. B
Potassium Ferricyanide 7 g
Water to make 100 ml

Mix 1+1
Notes:
1) This formula is present also in the first edition, dated 1908.
2) "If while mixing the liquid assumes a rather intense colour, you may let the solution decant and use the clean liquid, or add ¼ - ½ g of dichromate to the solution of ammonium iron citrate, which evidently was partially ferrous. To help the sinking into the paper while brushing the solution you may add to the ready-for-use recipe 10-20 g/litre of citric acid."
"Expose under a negative, immerse in water for 2'-3', wipe off with filter-paper and hang to dry. An immersion in chloridric or nitric acid 1% strenghths the blue, while solutions of sodium carbonate 2-5% or potassium oxalate 10% weaken it, if you want also locally."


E.J. Wall (1924)
Sol. A
Ammonium Iron Citrate green 12.5 g
Water to make 100 ml
Sol. B
Potassium Ferricyanide 4.5 g
Water to make 100 ml

Mix 1+1
Notes:
1) "Filter the solutions."
2) "The ferricyanide must be in ruby red and perfectly transparent crystals, without any yellow powder adhering...." (that is to say: pay attention to the presence of ferricyanure!)
3) "Brilliant prints can be obtained adding 0.5% of oxalic acid to the solution; the paper keeps better if you add 0.05% of potassium dichromate."


Clerc (1950)
Sol. A
Ammonium Iron Citrate green 36 g
Water to make 100 ml
Sol. B
Potassium Ferricyanide 16 g
Water to make 100 ml

Mix 1+1
Notes:
1) The same formula is in an English reprint of 1930.
2) In the Clerc's book the sensible solution is prepared dissolving the citrate and the ferricyanide (respectively 18 and 8 grams) in a total volume of 100 ml of water. I have converted the formula into two solutions because the conservation is enhanced; obviously in this way the concentrations in the two separated solutions must be doubled.
3) "Preparing the papers in this way, that with the green citrate needs more vigorous negatives than that prepared with the brown citrate."
4) "The ratio of opacities of a negative giving a blue deposit scarcely visible and producing a blue with the maximum density (measured after the washing of the print) are respectively of 47:1 and 34:1 for the green and brown citrate. The addition of a small amount of dichromate to the sensible solution allows printing less contrasty negatives."


Glafkidés (1958)
Sol. A
Ammonium Iron Citrate green 25 g
Water to make 100 ml
Sol. B
Potassium Ferricyanide 12 g
Water to make 100 ml

Mix 1+1
Notes:
1) pH < 2.3
2) "Adding small amounts of dichromate enhances the contrast. The triethanolammine (1cc) [in 200 ml of sensible solution, nor] increases the sensitivity and decreases the contrast."


These four formulae already show both different concentrations and ratio betwseen the two salts. As you will see below, the ratio between citrate and ferricyanide influences the contrast and the maximum density, so it is possible that these Authors would have tuned the process to fit the characteristics of their negatives and to met their personal tastes about the hue and saturation of the blues.

More considerations can be made after other formulae I have found in Internet.
The first is that some formulae have been repeated by many persons and in this case the most cited one is that also in "Coming into Focus" (8 citations); all the other have been cited by not more than three sites.
The second is that some formulae have been reported with rough roundings while converting from British and Metric units; for example I have seen cited "8 fl oz (250 ml) when 8 fl oz correspond to 227.4 ml instead. I do not know if who reported this formula adapted it to the British unit having found a metric original, but it is clear that these roundings give rise to unwanted variations. In the past, something like this had happened when someone thought that the weights were expressed as avoirdupois ounces and they instead were apothecaries ounces.
I have seen also errors due to a wrong conversion of the formulae, originally written for an unique solution, to adapt them to the two-separated-solutions version: sometimes the original amount were mantained, without considering that they must be doubled (see the case of the Clerc's formula).

Briefly, the above table shows the characteristics of the formulae I have found. The weight/volume concentration is referred to the sensible solution, as some formulae were written for an unique solution.
It must be pinted out that in some sites the mode of preparation and use of the solution is wrong or contradictory; for example someone indicates dissolving in certain amounts ow water, then using equal parts. In this and in other cases I have been able to calculate the concentration only in an approximate way.

The "historical" and yet cited formulae have been written first, while the other have been ordered as a function of the citrate concentration.

Fe. am. citr.
Pot. ferric.
Source
12.00  
3.50  

Namias 1908

6.25  
2.25  

Wall 1924

9.00  
4.00  

Clerc 1930

12.50  
6.00  

Glafkides 1958

10.00  
4.00  

Coming into Focus (John Barnier),
L' età del collodio (William Crawford),
W. J. Post-Factory Photogr.,5, 32 (2000),
jerryo.com/formula/CY_classic.htm,
phoenix.liunet.edu/~lawrence/photoche/cyanotyp.htm,
utopia.knoware.nl/users/vleeuwen/ctech.html, www.hands-on-pictures.com/Blueprint2.htm,
www.coloradocollege.edu/dept/ah/darkroom/non_silver.html,
www.cobb.k12.ga.us/~wheeler/arts/visart/TeacherResources/downloads/Photography/
CyanotypePrint.pdf,
www.photoshot.com/articles/general/ancient_printing_processes.htm
www.foto-sapiens.com/Helios/heliosf.html

5.00  
2.50  

photography.about.com/library/weekly/aa061801e.htm

6.00  
3.00  

www.astro.wisc.edu/~mukluk/blprint.html

8.33  
1.33  

personal.riverusers.com/~jdf/todd_walker/blueprint.html

10.00  
5.00  

www.ndirect.co.uk/~c.j.ball/formulae1.html

10.00  
6.80  

www.digitaltruth.com/data.html,
site.tekotago.ac.nz/staff/lgodman/drawing/info/Tech/Alternative/alt7.html

10.00  
7.00  

www.stanford.edu/~cpatton/yingui/cyano.htm
www.artic.edu/~fendsley/altProc_Blueprints.html,
art.arts.usf.edu/photo_area/lab/blueprin.htm,
www.azstarnet.com/~spacboy/cyanotype.htm

10.42  
7.29  

btc.montana.edu/nten/trc/lesson7/lesson7_text.shtml

10.60  
7.40  

cator.hsc.edu/~mollusk/ChemArt/photo/cyanotype.html

11.00  
5.30  

upnatom.com/cyanotype.html

11.00  
7.70  

Breaking the Rules (Bea Nettles)

12.50  
4.50  

www.stanford.edu/~cpatton/yingui/cyano.htm,
www.pipeline.com/~tomf2468/interclass5.html,
www.pipeline.com/~tomf2468/altinstruct04.html

12.50  
5.00  

Cyanotypes.com

12.50  
7.50  

altphoto.hihome.com/iron.htm

12.50  
12.50  

Creative Sunprinting (Peter Fredrick),
Antiche Tecniche (Giampaolo Bolognesi)

13.00  
4.60  

cyanotypes.com, www.nmpft.org.uk/insight/info/5.3.76.pdf,
www.photo.net/bboard/q-and-a-fetch-msg?msg_id=000rPm
National Museum of Photography, Film & Television BRADFORD, West Yorkshire

13.36  
6.68  

members.nbci.com/jormarge/.epb/cyano_page.htm,
www.greatbasinphoto.com/alt.html

15.24  
9.76  

www.dmuenzberg.de/cykassl.htm

18.00  
10.00  

www.photogs.com/bwworld/cyanotypes.html

26.96  
8.96  

jerryo.com/formula/cyanotyp.htm

33.33  
7.00  

rotoni.com/Cianotipia/


The only comment is that, as each author had satisfable results, the process is so flexible that it can tolerate wide variation of its formula. Nevertheheless, it must not be forgotten that each author has his preferences about the type of paper, the contrast of his negatives, and finally sometimes ... he is content with his results!

To sintetize the table and know something more you can look at the graphic here below.


(CIF = Coming into focus)

In the figure the lines corresponding to (from left to right) the ratio of 1:0.75, 1:0.6 (the theoretical ratio yet seen), 1:0.5 and 1:0.4 have been traced.

As can be seen, with the exception of two formulae, there is a ratio between citrate and ferricianide near or equal to 2, and it is preferred a concentration of citrate near or slightly higher than 10%.
It is probable that the most concentrated formulae work better with sized papers, and it must be pointed out that the practice of double coating the paper, as a fact, is almost equivalent to doubling the concentration. As a consequence, the amount of sensible matter per surface unit -this is what determines the density of the final image- has a much wider variation field.


5.  The Variables
To put into practice the aboveseen formulae, it must be remembered that these are only one part of the whole process for the production of a cyanotype. The process, as it is known, consists in:

  • choosing the paper
  • preparation of the mother solutions

  • coating of the paper

  • drying

  • exposition

  • washing

  • drying


    • Each step, like for other O.T., may have effects on the final result.

    As it has been told, the ammonium iron citrate is not a well defined substance, and it may contain various impurities, among these some residuals of divalent iron; this leads to the formation of the Turnbull blue before the exposition and consequently the veiling of the whites.
    Forthermore, Clerc suggests washing the ferricyanide crystals from the eventual yellowish crust covering them (note 4).
    Hence the manufacturer and perhaps also the age of the two substances (hence their purity) may lead to results different than they are expected.

    Many modern authors and photographers note different results when changing type of the paper, both in term of hue and of sensitivity. As a consequence we cannot exclude that the different formulations proposed since the last century may be the result of a personal adapting to oneself operating condition, which are the purity of the substances, the paper, the quality of the water, etc..
    In fact, the Turnbull blue is soluble in alkaline solutions and hence also eventual alkaline buffers present in the paper -used to enhance the conservation of the paper- or an excess of calcium (hardness) of the tap water may lead to the fading of the cyanotypes.

    The penetration into the paper fibers is another variable influencing the final result, and it is usually determined by the paper sizing. On the contrary of other processes, usually it is not necessary to size the paper; if one wants, it is suggested to use albumine or starch, but not gelatine. Another trick used when dealing with too much adsorbing papers is adding 3% of gum arabic to the sensitizing solution (Seigel 2000b).
    On the contrary, it is almost ever preferable having a good penetration of the solution into the paper, and for this purpose it is sometimes suggested to add a sufactant or to dilute the sensitizing solution (Ware 1996).

    From what has been written above, it would not be surprising that it has been reported (Seigel 2000b) that some papers, among these Arches Aquarelle and Fabriano 5, fit well the cyanotype, or that some other, among these Fabriano Artistico, tend to be contrasty or low in contrast (Arches Platine).

    Like for other processes, the sensitized paper must be used as soon as possible. It has been reported (Seigel 2000c) that temperature and humidity give rise to different times of decay of the sensitized layer (few hours in hot climate, some days in dry and cold climate); however also this amount is paper-dependant.

    Among the methods to vary the contrast there are cited (Seigel 2000c) the double coating, the addition of oxalic acid and/or dichromate, the variation of the ratio between citrate and ferricyanide, the acid washing before the sensitization and the acidification of the washing water.
  • The double coating gives deeper blues, but also tends to give more contrasty prints.

  • The dichromate (i.e. 1%) in the first washing water tends to darken the shadows and to bleach the middle tones and the highlights. The same if the dichromate is added to the sensitizing solution (2%).

  • The acidification of the paper with 1% acetic acid, or 5-10% potassium alum, or 1% oxalic acid gives rise to a wider tonal scale and to deeper blacks without staining the whites.

  • The acidification with 4-5 dops up to some ml of hydrochloric acid in one litre of water has been suggested to prevent the loss of colour and the staining of the whites. In addition, this practice helps the removing of the last traces of iron salts which, with the time, would stain the paper (Bolognesi 1994).


    • The addition of hydrogen peroxide to the last washing water, in order to deepen the blue, seems not strictly necessary as the exposition to the air leads to the same result in a few days.


    Concluding this brief and not-exaustive sight, all should suggest us to make some tests with our own materials, and to keep accurate notes about the various tested combos in order to finid that with the best results. Finally, using a step tablet is highly recommended for simplifying the comparisons.


    6.  Recipes from the Members
    A brief enquiry among the GRN members making cyanotypes confirmed different choices both for the base formula and the other variables.

    The following table resumes those differences (concentrations refer to the weight/volume mix and to the separated solutions, if not differently indicated).

    Author
    Fe NH4 citrate
    K ferricyanide
    Paper
    Washing
    Notes
    Berger
    3
    (see notes)
    1
    (see notes)

    Bockingford 535 g/m²

    5 drops hydrochloric acid /litre

    dissolve the amounts in grams in 20 ml of water; the solution covers a sheet 20x30cm
    paper sized with gelatine 5%

    Bolognesi
    25
    25

     

     

     

    Bottani
    20
    8

    Fabriano F5
    Fabriano Artistico

    		 

    The most intense blue, almost black, has been obtained with unsized paper and without the lead acetate toning sometimes used for other papers

    Gazzarri
    25
    25

    Fabriano F4 satin

    hydrochloric acid,
    max 5 ml/litre

    Hydrogen peroxide in the last washing

    Novo
    25
    25

    Arches Aquarelle

    hydrochloric acid,
    5 ml/litre

    Double coating on unsized paper

    Valentini
    20
    8

    Fabriano F4,
    Fabriano Rosaspina,
    Canson

     

    Unsized paper


    7.  Conclusions
    The ideal formula does not exist. There are, instead, some combos sensible solution/paper/negative which give results better than other. This is probably the motive of so many formulae which have been found; however, the taste and personal aesthetic sense play a primary role in judging the winner.
    Everyone is thus encouraged to continue his way if he is satisfied with his results, or to verify through some simple tests if there is a better combo.

    In a future article I will present the results of some laboratory tests comparing, under controlled conditions, some combos among the many possible ones.


    Alberto Novo            




    NOTE

    1)  The cyanotype has been the first photographic process on paper, as it was noticed by Sir John Herschel in 1842, but the blue colour of the images -the only one which could be obtained- made that process not competitive with the daguerreotype.
    The first practical application of this process was in 1843 with the book of Anna Atkins "British Algae: Cyanotype Impressions", which someone defned "the first photographic book" (the date of "The Pencil of Nature" of Talbot is 1844). Anna Atkins, a botanics scientist, printed the shadow (nowadays we would say a photogram) of vegetal specimens conserved in an herbarium for scientific purposes, probably to complete the book without images "Manual of British Algae" of William Harvey. Anna Atkins' book was published again many times till 1853 and coupled with another book, obtained with the same technique, devoted to mosses and firns.

    2)  The Prussian Blue was named in this way as it has been used to dye the uniforms of the Prussian army. It is known also as Hamburg, Paris, Harlem, oriental, potash blue, etc.
    The history of the Prussian blue has the taste of a metropolitan legend. "It is said" that a German dye producer named Diesbach discovered by chance in 1704 the way to prepare this pigment starting with ox blood, but thinking to make a red pigment like the starting material. Diesbach's shop-boy begun preparing this pigment in Paris, and the Dutch painter Simon Eikenlenberg wrote in 1722 some notes on how to prepare it. In 1724 the process went in England and its detailed preparation description was printed in 1764 ina manual for artists.
    The preparation process begins heating to red heat equal parts of saltpetre (potassium nitrate) and cream of tartar (potassium tartrate) in a crucible. Dry ox blood is added to the mix, heating it up to incandescence. The mass is washed with water and treated with a solution of alum (potassium aluminium sulphate) and green vitriol (ferrous sulphate). A green precipitate is formed, which turns into blue adding muriatic acid (hydrochloric acid).
    J. Copelandand e C. Rochelle (1998)
    In http://www.sewanee.edu/chem/Chem%26Art/Detail%5FPages/Pigments/Prussian%5FBlue

    3)  Prusian blue and Turnbull blue are so coloured because of the configuration of their molecula.
    Both dissolve in concentrated mineral acids, but are resistant to the diluted one up to 10%, to the polar and not polar solvents, to the oils and plastifiers.
    The pigment is so finely subdivided in colloidal aggregates that it has the characteristics of a dye. The colour is permanent to the air for a long time, also if sometimes it may give a bronze shadow if it is exposed to weathering.
    The pigment is sensible to alkaline substances, which turn it brown.
    J. Copelandand e C. Rochelle (1998)
    In http://www.sewanee.edu/chem/Chem%26Art/Detail%5FPages/Pigments/Prussian%5FBlue

    4)  "Rincer les cristaux de ferricyanure pour les débarasser de leur crôute ocreuse".
    Clerc, L.P. (1950) "La Technique Photographique"
    5th Ed, tome II, Publications photographiques et cinematographiques Paul Montel, Paris V, 1950, nota a pie' pag. 816 

    torna al testo di provenienza

    8.  Bibliography

    Abrahamson, H.B. (1999) "The Photochemical Basis of Cyanotype Photography"
    J. Chem. Educ., 1999, 76, 1199-1200
    reperibile come abstract in
    http://jchemed.chem.wisc.edu/Journal/Issues/2001/Mar/abs311_2.html 
    Bolognesi, G. (1994) "Antiche Tecniche"
    Collana Manuali di Fotografia di Tutti Fotografi, p.51 
    Clerc, L.P. (1950) "La Technique Photographique"
    5th Ed, tome II, Publications photographiques et cinematographiques Paul Montel, Paris V, 1950, pp.816-817 
    Glafkides, P. (1958) "Photographic Chemistry Vol. One"
    trans. K. Hornsby; Fountain Press, 1958 
    Hylen , M. (2000) "Cyanotypes. A New Look at an Old Technique" Thesis published at Central St. Martin's school of graphic design, MA, 2000
    http://cyanotypes.portland.co.uk/cthesis.html
    Kleinke, H. (2001) "Metal Chemistry. Inorganic Transition. Class notes 6: Isomerisms and reaction mechanisms"
    http://www.science.uwaterloo.ca/course_notes/chemistry/chem310/2001_6.html 
    Namias, R. (1929) "Chimica Fotografica"
    VII Edizione; Il Progresso Fotografico, Milano 1929. Vol. II, p.204 
    Scheimreif, S. (2000) "Diploma Physical Science. Answer to: What is the toxicity of ferrocyanide and ferricyanide ions?"
    http://www.sci-ctr.edu.sg/ScienceNet/cat_physical/cat_che010508.html 
    Seigel, J. (2000a) "Random notes on exposure, cyanotype & so forth..."
    The World J. of Post-Factory Photogr., Issue#5, p.30 
    Seigel, J. (2000b) "Cyantifically speaking: about the paper"
    The World J. of Post-Factory Photogr., Issue#5, pp.38-40 
    Seigel, J. (2000c) "Managing the blues"
    The World J. of Post-Factory Photogr., Issue#5, pp.34-37 
    Wall, E.J. (1924) "Photographic Facts and Formulas"
    American Photographic Publishing Co., Boston, Mass., 1924 
    Ware, M. (1996) "The New Cyanotype Process"
    http://www.mikeware.demon.co.uk/cyano.html 
    Ware, M. (1999) "Cyanotype. The History, Science and Art of Photographic Printing in Prussian Blue"
    National Museum of Photography, Film & Television; Bradford, UK, 1999. (208 pp.) 

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