Uranotype and Wothlytype

☠Level D, and the clearest case of exclusion on hazard alone

The glossary’s own judgement of the uranotype is the one this entry is built around: it is the clearest case in the course of a process excluded on hazard rather than on difficulty or cost, and of the course’s rule that a hazard it cannot fully read is a hazard it does not hand over.

No procedure appears here, and none appears anywhere else in the course. The entry exists so that a reader who meets the process in a collection knows what they are looking at.

The register names these two together as one row, and this entry follows it. What they have in common is that the light-sensitive material is a uranium salt rather than silver or iron — which puts them outside every family this atlas is otherwise organised by.

The chemistry

Light reduces the uranium, and the reduced uranium then does something else. Vogel’s 1875 textbook describes nitrate of uranium as reduced by light to a sub-nitrate in the presence of organic bodies such as a paper support, giving an image so faint as to be scarcely perceptible — then made visible by plunging the sheet into a silver or gold solution, where the reduced uranium precipitates the metal as a brown or violet powder.

Read the structure of that and it is a siderotype with uranium in the iron’s place: a photochemically reduced metal salt that is not itself the image, acting as a reducing agent for a noble metal that is. The argentotype and chrysotype do exactly that with iron.

The spectral behaviour is the other half. The 1911 Encyclopaedia Britannica adds that uranium salts are acted on only by the light they absorb, the nitrate absorbing in the green-blue — which is unusual in this atlas, where almost every process is driven by ultraviolet and violet.

And a second route develops with a ferricyanide. The glossary records that development is commonly with a ferricyanide, which is the same chemistry as uranium toning run as a printing process rather than as a treatment. Eder worked that scheme out in 1876: metallic silver, or here a reduced uranium species, reduces ferricyanide to ferrocyanide, and the ferrocyanide forms an insoluble coloured compound with the metal ion present.

!How much of this entry is unfilled, and why

The front matter above leaves surface, tonal scale and permanence empty, and the date carries a note saying the course does not settle it. Those are not oversights.

The corpus behind this course holds uranium chemistry in some depth as a toner and intensifier — the uranyl nitrate entry and Kodak IN-21 — and it holds two short accounts of the printing processes, in Vogel and in the Britannica. It does not hold a description of a finished uranotype as an object: its colour measured, its surface, its scale, or how a conservator identifies one beyond the uranium’s own X-ray fluorescence line at 13.61 keV.

Filling those fields with plausible values would be inventing a process history, which Rule 1 forbids. A later author with the conservation literature to hand should treat this as a correct skeleton rather than as a finished account.

Historical workflow

Sensitise paper with a uranium salt; expose under a negative to a scarcely perceptible image; develop by immersion in a silver or gold solution, or with a ferricyanide; wash. That is the whole of what the corpus supports, and it is stated as history rather than as a sequence to follow.

The Wothlytype is named beside it in the register and in the glossary as the same family, and this course has read no separate account of it. It is recorded here as a name a reader will meet rather than as a process the course can describe.

The image

Handsome, on the sources’ own testimony, and unquantified here. The glossary says the chemistry is real and the prints are handsome; Vogel gives brown or violet where the reduced uranium precipitates silver or gold. Beyond that the course has nothing measured.

One identification is solid. Uranium is easy to find afterwards by its L-alpha line at 13.61 keV under X-ray fluorescence, which the Getty atlas records in the context of uranium-toned platinum prints and which applies equally to a uranium-printed one.

Permanence

Not established here for the printing processes.

What the course does know is the behaviour of the neighbouring treatment, and it is not encouraging. The uranium ferrocyanide deposited by uranium toning is soluble in alkalis, so long washing in ordinary water reduces the colour, and an alkaline bath removes it. If the printing processes deposit a related compound then they inherit that vulnerability — but the course has not read a source that says they do, and it does not transfer the finding.

Hazards

Uranium, and the Level D policy names it as one of the families the level covers. Uranyl nitrate hexahydrate is photography’s one radioactive reagent, and its encyclopaedia entry is classified Level D on that basis. Princeton’s environmental health guidance lists uranium nitrate among the older, discarded intensifiers, in the same sentence as the mercury ones.

A waste stream with no domestic answer. A bath carrying a soluble uranium salt is not something a household waste route can accept, and the course’s disposal caveat applies with more force here than almost anywhere else in the atlas.

And a hazard the course cannot fully read. The glossary’s phrasing is deliberate and worth repeating: this is a case of the course’s rule that a hazard it cannot fully read is a hazard it does not hand over. Radiological assessment is outside the competence this course claims, and the honest response to that is to describe and refuse rather than to assess badly.

For a reader who owns rather than makes one, the practical consequence is the one the glossary names: a uranium print in a collection is a radiological question and not only a conservation one, which is why the identification line above matters more here than for most processes.

Why we study it and do not reproduce it

Because a reader meeting one in a collection needs to know what it is. That is the glossary’s own stated reason for the entry existing, and it is the strongest one.

Because it completes the picture of what light can be made to reduce. Silver, iron, gold, platinum, palladium, mercury, chromium — and uranium. A reader who has followed the siderotype family through four metals has the pattern; this is the member of it the course refuses.

And because the reason for the refusal is different from every other refusal in this atlas. Platinum is refused because sensitisation is irreversible; the daguerreotype because mercury vapour is invisible and unsmellable; the dichromate family because of a standing policy; collodion because of ether. Uranium is refused because the course cannot competently assess the hazard at all, which is a different kind of answer and worth having in the atlas once, stated plainly.

Where the course carries it, and it carries no steps. Part XXVI owns it, in Uranium, Mercury and the Heavy-Metal Treatments, which teaches the whole heavy-metal family as chemistry and history with no procedure — the rule of the part rather than a limitation of this row.

And the lesson confirms this entry’s central claim in the exact terms it was made. Its section Why uranium is excluded, stated carefully separates the two hazards and says why only one of them can be read: the chemical hazard presents as kidney injury and is fully described — a NIOSH symptom list, a recommended limit of 0.05 mg/m³ as uranium, and a notified classification on uranyl nitrate of Danger, fatal if swallowed and fatal if inhaled. The radiological hazard is described nowhere in that record: no GHS classification covers it, EH40 does not list uranium at all, and NIOSH attributes the cancer potential to alpha emission and decay products rather than to the chemistry. A control cannot be specified against a hazard that has not been characterised — which is this entry’s argument, stated by the part as the reason for the level and as a different reason from every other exclusion in it.

The lesson adds two cautions this entry should be read with. The reading that chemical toxicity dominates at photographic quantities is labelled as the course’s own inference, not a source’s conclusion. And the one radiological figure in the corpus — the Getty’s roughly 117 µREM per hour about a centimetre above a uranium-toned print, against a background near 10 — is a measurement of a finished object with the uranium embedded in gelatin, and must not be carried across to weighing the salt or drying a residue on a bench. There is also a second regulatory regime, unrelated to photography or waste chemistry, which the lesson reads from the Environmental Permitting Regulations 2016 with three stated limits on its own reading.

The history is fuller than this entry could make it, and one term needs correcting. Ware’s account gives Burnett of Edinburgh the uranium printing processes in 1857 and the first palladium prints in 1856 — sixty years before Willis’s palladiotype, on entirely different photochemistry — with none of his prints known to survive, and records Niepce de Saint-Victor’s 1858 publication and Burnett’s accusation of plagiarism. Cassell confirms the Wothlytype’s composition from 1911 and the Getty confirms it from the objects: silver, gold and uranium in a collodion binder, the uranium being the signature that separates it from the ordinary collodion rows. And uranotype is a collective name rather than one process — Cassell applies it to the uranium, mercuro-uranotype and platino-uranotype processes alike — so a reader meeting the word in a catalogue should treat it as a family label. This entry holds the identification fields for that family.

Two verdicts on the Wothlytype stand together rather than against each other: Ware’s “egregious and unsuccessful”, which judges it as a product, and Cassell’s “practically the immediate predecessor of collodio-chloride printing-out papers”, which judges it as a lineage. A silver salt in collodion, printed out and gold toned, is structurally the collodion printing-out paper of the 1890s minus the uranium.

The additive form of the same chemistry — uranium put into a process the course does print — is collected in Part XXV’s Level D lesson, and Part XXI records Ware’s own test of the uranyl claim in a cyanotype sensitiser: about one stop of speed, and not worth the toxic risk.