Blog
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Cyanotypi
Cyanotypi er en fotografisk printproces, der udnytter jernsalte til at producere et karakteristisk blåt billede. Denne artikel beskriver de grundlæggende kemiske reaktioner i cyanotypidannelsen, efterfulgt af metoder til billedblegning og efterfølgende omfarvningsteknikker for at ændre printets æstetiske egenskaber.
Grundlæggende om Cyanotypiprocessen
Cyanotypiprocessen involverer sensibilisering af et substrat, typisk papir, med en opløsning af ferriammoniumcitrat og kaliumferricyanid. Ved eksponering for ultraviolet (UV) lys reduceres ferrijernet (Fe³⁺) i ferriammoniumcitratet til ferrojern (Fe²⁺) i de områder, hvor lyset rammer. Dette ferrojern reagerer derefter med kaliumferricyanidet og danner uopløseligt berlinerblåt (ferriferrocyanid, Fe₄[Fe(CN)₆]₃). Efterfølgende vask i vand fjerner ueksponerede kemikalier og efterlader et stabilt, permanent blåt billede.
Blegning af Cyanotypibilleder
Blegning af cyanotypibilleder er en kemisk proces, der anvendes til at reducere eller helt fjerne det berlinerblå pigment fra substratet. Dette opnås typisk ved brug af alkaliske opløsninger, såsom natriumcarbonat eller ammoniak, der omdanner det uopløselige berlinerblå til opløselige ferrocyanidkomplekser, som kan vaskes væk. Alternativt kan oxidationsmidler som husholdningsblegemiddel (natriumhypochlorit) eller oxalsyre nedbryde pigmentet direkte. Graden af blegning styres af blegemidlets koncentration og nedsænkningstiden, hvilket resulterer i et falmet eller helt hvidt billede.
Omfarvning af Blegede Cyanotypier
Omfarvning indebærer at introducere ny farve til et bleget cyanotypiprint. Efter det berlinerblå pigment er fjernet, er substratets fibre modtagelige for forskellige farvestoffer. Almindelige omfarvningsmetoder inkluderer nedsænkning i opløsninger af botaniske ekstrakter (f.eks. te, kaffe, gurkemeje) eller syntetiske farvestoffer. Papiret absorberer farvestoffet og giver billedområdet og selve substratet en ny nuance. Den endelige farve afhænger af det valgte farvestof, dets koncentration og interaktionen med cellulosefibrene.
Den sekventielle anvendelse af cyanotypiprint, kemisk blegning og efterfølgende omfarvning udgør en omfattende metode til manipulation af fotografiske print. Disse processer muliggør præcis kontrol over billedtonalitet og farve, der rækker ud over den iboende blå farve i traditionelle cyanotypier.
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Creative Coding: by tekiela
Generative art is deeply rooted in the history of computing. Discover how algorithms recreate the nostalgic, calming charm of late-70s CRT displays. At Creative Code Denmark, Jacob Tekiela dives deep into these programmatic techniques, showcasing vintage aesthetics mathematically generated in modern tools.
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Cyanotype
Cyanotype is a photographic printing process utilizing iron salts to produce a distinctive blue image. This article details the fundamental chemical reactions of cyanotype formation, followed by methods for image bleaching, and subsequent re-dyeing techniques to alter the print’s aesthetic properties.
Cyanotype Process Fundamentals
The cyanotype process involves sensitizing a substrate, typically paper, with a solution of ferric ammonium citrate and potassium ferricyanide. Upon exposure to ultraviolet (UV) light, the ferric iron (Fe³⁺) in the ferric ammonium citrate is reduced to ferrous iron (Fe²⁺) in areas where light strikes. This ferrous iron then reacts with the potassium ferricyanide to form insoluble Prussian blue (ferric ferrocyanide, Fe₄[Fe(CN)₆]₃). Subsequent washing in water removes unexposed chemicals, leaving a stable, permanent blue image.
Cyanotype Image Bleaching
Cyanotype image bleaching is a chemical process employed to reduce or entirely remove the Prussian blue pigment from the substrate. This is typically achieved using alkaline solutions, such as sodium carbonate or ammonia, which convert the insoluble Prussian blue into soluble ferrocyanide complexes that can be washed away. Alternatively, oxidizing agents like household bleach (sodium hypochlorite) or oxalic acid can directly degrade the pigment. The extent of bleaching is controlled by the concentration of the bleaching agent and the immersion duration, resulting in a faded or completely white image.
Re-Dyeing Bleached Cyanotypes
Re-dyeing involves introducing new color to a bleached cyanotype print. After the Prussian blue pigment has been removed, the substrate’s fibers are receptive to various coloring agents. Common re-dyeing methods include immersion in solutions of botanical extracts (e.g., tea, coffee, turmeric) or synthetic dyes. The paper absorbs the dye, imparting a new hue to the image area and the substrate itself. The final color is dependent on the specific dye chosen, its concentration, and the interaction with the cellulose fibers.
The sequential application of cyanotype printing, chemical bleaching, and subsequent re-dyeing provides a comprehensive methodology for manipulating photographic prints. These processes enable precise control over image tonality and color, extending beyond the inherent blue of traditional cyanotypes.
