The invention

Puhar built upon the already known daguerreotype process.

His modest income prevented him from successfully experimenting with the daguerreotype process. The required silver-coated copper plates were too expensive and it was not in his nature to just copy what others have discovered before him.

In his photography-related work, Puhar only used material that was cheap and readily available: glass plates, bromine, sulphur, iodine, mercury and alcohol.

In a bright environment, Puhar first cleaned a small regular glass plate. He then lit a sulphur stick of his own invention. The sulphur was mixed with mastic, a natural resin that was adhesive and soluble in alcohol or ether. This mixture was then used to imbue a piece of the pith of a common rush, which was combustible. The resulting product was inserted into a narrow metal tube that allowed enough air for combustion. The rising sulphuric vapours covered the glass plate that had to be held over a flame. The plate was now coated with a pearl white layer and had a bluish red translucent character under light.

The plate coated with a transparent layer of sulphur was then exposed to iodine vapours in a dimmed environment. Afterwards, the prepared glass plate was inserted in a specially prepared base on the back of the camera. Puhar then chose a motif in the light and set the focus using the adjustable part on the back of the photographic camera. After that, he poured mercury into a metal container and placed it on the bottom of his camera. He then heated the mercury so that it would produce vapour. Puhar used lenses made from regular glass that had a 2 inch focal length.

The prepared plate was then exposed to light for one minute, but later only fifteen seconds were necessary to achieve the same result. The exposure would start the chemical process in which the mercury vapours coated the exposed places on the picture. The amount of mercury would be greater in those places on the picture which received more light. The picture on the glass in the camera was faint which is why Puhar had to strengthen his mercury picture created on a sulphur-iodine base with bromine vapours. The resulting negative on glass was then fixed in alcohol. His photographic process was dry - he only worked with vapours. The entire process lasted between 5 and 8 minutes.

The result was a negative in a nice bluish tone. Puhar instructed the pictures to be exhibited on dark backgrounds as this was the only way for our eyes to recognise the original negative picture on the glass as a positive. Puhar varnished his pictures and turned the glass plates around, so that the motifs on them were not mirror images. This was an exceptional development in the time of the daguerreotypes, the drawback of which was that they created mirror images. At the end of the process, Puhar laid another glass plate on top of the first glass plate and sealed the edges in order to protect the picture from humidity and dust. Each picture on glass was unique.

Puhar continuously improved his original process. He later replaced the term "helyotipija" with "hyalotipija", which means "image on glass" or "svitlopis". He finally used "svetlopis", which means "light-writing".

His process has still not been replicated and therefore Janez Puhar the inventor remains an enigma to this day.

Illustrations: Zoran Smiljanič

"Novo odkriti postopek za izdelavo prosojnih heliotipij na steklene plošče", Puharjevo besedilo, objavljen v Carniolii 28. aprila 1843 "Prosojne slike na steklo", Puharjevo besedilo, objavljeno v Poročilih dunajske Akademije iz leta 1851

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December 18