Based on 'Rock glazes of NZ'
Sample 92: Weathered Schist, Sand near Picton
Slightly weathered Schist similar to the schist widespread in Central Otago. Probably fairly close to Greywacke in chemical composition.
In Bondy's book Rock glazes of NZ, there is no exact place documented where samples were collected.
After talking to Ann her daughter over the weekend I know they stayed at campsites. Ann was less than enthused on the trip as her brother had a water pistol and continued to harass her with it. Her mother's solution to the back seat fighting was to also buy Ann a water pistol.
Although it's a rough assumption, I figured with two young children fighting in the back seat, she may have collected samples in camping areas where they stayed. This spot Whatamango bay fitted the brief, 'near Picton' and 'slightly weathered Schist'
Bondy had the help of geologist Dr W. Waters who she acknowledges in her book. There were also early geographic studies into this area to go off at the time.
Since the 1960's there has been further research into the sounds, particularly how ferries and logging affect the marine environment. The Lauder Thesis Coastal landforms and sediments of the Marlborough Sounds and Broad-scale survey of Whatamango Bay estuary 2018
confirmed for me that this bay is predominately schist deposits. A mix of particles, inorganic and organic, gravelly, sandy and muddy. Predominately schist with the source being the flow of the Pelorus River.
Sourcing this mud was ingenious as nature has done the majority of the grinding. As you can see in the photos the rusty coloured iron deposits are present, so a "brown" glaze is most probably the outcome. I'm curious to see what other properties it shows in the results.