Month: July 2019

The Meg

Often an object has a much wider story to tell than what can be seen at face value, as interesting as that can initially appear.  Part of the fun in researching it is uncovering the wider back story which helps to build up a bigger picture of where we stand at the present.

So with that in mind, how did a tooth from a megalodon end up in the riverbed near Whanganui?

2. Megalodon size

The Megalodon at the top, compared to a Great White Shark and a Human. Image sourced through Creative Commons.

The largest known shark, the Carcharodon megalodon lived from 16-2.5 million years ago. The megalodon was related to the Great White Shark of today but was huge. Fossil remains show the megalodon was an average size of 10.5 metres long but could grow up to 18 metres. An adult human could easily sand up in its jaws which measured over two metres wide.

The particular tooth in the Museum collection measures 13.5 centimetres high and 11.5 centimetres wide. It was found near Pīpīriki in a bank of sandstone estimated to be four to five million years old. Because of its marine past, Whanganui is a great place to find marine fossils, in particular fossilised shark teeth.

1. Megalodon tooth

The Megalodon tooth found near Pipiriki. WRM Ref: 1800.175

About 540 million years ago, New Zealand was being formed on the eastern edge of the supercontinent Gondwana. This continent included what we know today as Australia, Antarctica, India, Africa and South America.

Around 100 million years ago, hot rock began to accumulate underneath Gondwana and move towards the edges of the land, pulling it apart. This slowly made a giant rift which allowed the sea to flood in, and separated it from the mainland, thus creating the continent of Zealandia. After breaking away from Australia around 85 million years ago, Zealandia largely sank beneath the Pacific Ocean. What remains visible today is essentially the highlands of the continent, and the rift is now the Tasman Sea.

Zealandia sits across the edge of the Australian and Pacific tectonic plates and is slowly being broken up as they continue to move. The last 1.8 million years have shaped the land with tectonic movements, glaciers and volcanoes, altering the landscape. Whanganui, being on the coast of New Zealand and consisting of lifted sea beds, is more likely to reveal marine fossils.

The hinterland areas are fertile with volcanic ash at the core. The mountains in the north and west help to shelter the township and have created a wonderful climate, much warmer and drier compared to other coastal towns.

Before human settlement, this land was covered with forest: tōtara, matai, rimu, tawa and beech trees covered the landscape. The soft rock near the coast was easily worn down by water, and helped to create the Whanganui River, the longest navigable waterway in New Zealand, measuring 290 kilometres from its source at Mount Tongariro.

All this adds up to a beautiful place with fertile lands, fresh water, ocean access and a temperate climate, which made it perfect for settlement when Māori arrived.

 

Sandi Black is the archivist at Whanganui Regional Museum.

Ambrotypes

Another post here discusses photographic daguerreotypes, so let’s now look at the next step in the development of photography.

Whereas the daguerreotype produced a negative image on a metal base, an ambrotype created a positive image on glass. The ambrotype is a variation of the wet plate collodion method introduced by Englishman Frederick Scott Archer in 1851.

For the wet plate collodion method, a glass plate was polished and coated with a thin layer of iodized collodion before being dipped in a bath of silver nitrate solution for three to five minutes. Once it had drained and dried, it was placed in a plate holder with a dark slide to protect it from the light.

1. Woon Brothers

 Ambrotype of four of the sons of the Reverend William Woon
Date unknown. Left to right: Garland William, James Garland, Edwin Turner, and Richard Watson Woon. WRM Ref: 1988.35.1

The prepared plate was loaded into the camera while still wet and the dark plate removed to begin exposure, which could take as little as five seconds, or well over a minute, depending on the light and conditions of the day. Once done, the dark slide was replaced and the plate removed from the camera for immediate treatment – it could not wait or the image would be lost. It would be developed using a ferrous sulfate developer, and the image would be fixed with potassium cyanide or sodium thiosulphate solution before being rinsed and varnished.

The resulting image looked like an underexposed negative, but would appear as a positive when viewed against a dark background. The dark areas of the image appeared as clear patches on the plate while the lighter areas of the image showed opaque. The glass plates were often painted black on one side or mounted against black velvet to make the image easier to see. They were monochrome but could be hand coloured.

2. Mr Keen

 Ambrotype of Mr Keen, a stable keeper with premises on St Hill Street. 1869. WRM Ref: 1955.74.1

Another plate of glass would be mounted over the emulsion side before the plates were mounted within a metal frame and housed in a case, just as daguerreotypes were.

Ambrotypes were significantly cheaper to create than daguerreotypes. The plates did not need to be polished or fumed, which reduced equipment and material costs, and they were made out of much cheaper glass rather than expensive silver-plated copper. It was also possible to photograph more clients per day, due to the reduced exposure time.

There were, however, disadvantages. The technique required great dexterity as the whole process had to be completed within 10 minutes before the plate dried, so ambrotypists had to have a dark room immediately available. Travelling ambrotypists would take a tent or portable dark room with all the associated chemicals with them.

3. Unidentified woman

 Ambrotype of a young woman, with hand coloured background and jewellery accented with gold pigment. Date unknown. WRM Ref: 1977.33.19

The nitrate bath solution could leave stains on clothing and furnishing, and the plates could leave nitrate residue in the camera. An overload of nitrate could be potentially explosive.

The photograph fixer, potassium cyanide, was a powerful, deadly poison, and occasionally caused cyanide poisoning. It was even drunk by one photographer to commit suicide.

Ambrotypes were still relatively quick and significantly cheaper than daguerreotypes and became immensely popular between 1855 and 1865. There are many more ambrotypes than daguerreotypes surviving today, 32 of them in the Whanganui Regional Museum collection.

 

Sandi Black is the Archivist at Whanganui Regional Museum.