Question: What kind of negatives are the Holtermann collection that showed a former gold mining town in New South Wales?

Context paragraphs:
Gulgong Holtermann Museum: Gulgong Holtermann Museum is a community project and a museum space located in gold rush town of Gulgong, New South Wales.  Two of the town's earliest buildings are to house an interactive educational and tourist facility based on the UNESCO listed Holtermann Collection - photographs taken for Bernhardt Holtermann during the "roaring days" in the 1870s.

Independence Mines: The Independence Mines, now Independence Mine State Historic Park, is the site of a former gold mining operation in the Talkeetna Mountains, across Hatcher Pass from Palmer, Alaska.  The area's mining history dates to at least 1897, when active claims were reported in the vicinity of Fishook Creek.  These early mining efforts were eventually joined to form the Wasilla Mining Company, which worked the mines from 1934 to 1943, and again from 1948 to 1950.  The mining operation at Independence was the second-largest hard-rock gold mining operation in the state, after a larger site near Juneau.  The company and the miners that preceded it built a substantial mining camp, with as many as sixteen wood frame buildings, which were originally connected to each other by sheltered wooden "tunnels".  When the company ended operations in 1950, it had expected to eventually resume operations, but never did; this resulted in a particularly well-preserved collection of mining equipment and buildings, although the weather has since taken a significant toll on the latter.

Hill End, New South Wales: Hill End is a former gold mining town in New South Wales, Australia.  The town is located in the Bathurst Regional Council local Government area.

Holtermann collection: The Holtermann Collection is the name given to a collection of about 3,500 glass-plate negatives which mainly depicts life in the New South Wales goldfields towns of Hill End, Gulgong, Home Rule and Canadian Lead.  Photographs of people and prominent landmarks are also included.  The photographs were taken in the second half of the nineteenth century.  The collection is held by the State Library of New South Wales.

Weaver, Arizona: Weaver, or Weaverville, is a former gold mining town, now a deserted ghost town, in Yavapai County, Arizona.  All that remains are some rusting mining machinery, a partially restored cemetery, and the ruins of a stone house.

Hanging Rock, New South Wales: Hanging Rock is a gold mining village and also rock face on the Northern Tablelands, New South Wales, Australia.  This former gold mining town is situated about 10 km south east of Nundle.  The village is part of the Tamworth Regional Council district and Parry County.  Hanging Rock's geographical coordinates are 31° 29′ 0″ South, 151° 12′ 0″ East and the elevation is about 1100 m. Due to the high altitude of the village, Hanging Rock and the surrounding mountains can occasionally receive a snow fall on the coldest of winter days.  At the 2006 census, Hanging Rock had a population of 195 people.

Yugarenok Airport: Yugoryonok is a disused airport in Russia located 1 km north of Yugoryonok, a former gold mining town.  With the cessation of most of the gold mining activity in the area in the 1990s, the airport was closed.

Plains of Leon: Plains of Leon, named for the former gold mining town, Leon once located near the middle of the plain.  It is a plain in the Perris Block, contiguous on the south with the Perris Plain including within it the Domenigoni Valley and western Diamond Valley, French Valley, Auld Valley, the upper part of the valley of Warm Springs Creek and connecting tablelands.

Shire of Mount Morgan: The Shire of Mount Morgan was a local government area located in the Capricornia region of Central Queensland, Queensland, Australia, about 20 km south of the regional city of Rockhampton.  The shire, roughly the region surrounding the former gold mining town of Mount Morgan, covered an area of 492.0 km2 , and existed as a local government entity from 1890 until 2008, when it amalgamated with several other councils to become the Rockhampton Region.

Bradford, Victoria: Bradford is a small town located near the former gold mining town of Maldon, Victoria.

Supporting paragraphs: Holtermann collection Hill End, New South Wales
Answer: glass-plate