Based on 'Rock glazes of NZ' Minna Bondy Sample 14. Iron Sand
Ordinary black sand. many of the grains are strongly magnetic, low in silica and alumina but high in iron oxide and titania.
The black sand was the hardest of all the test materials to apply as a glaze.
Most of the other samples mixed well with the ash and the calcite. However, the black sand separated from water content and this made it difficult to adhere and absorb into the bisque ware, resulting in it brushing off easily.
It was also the only sample to adhere to the kiln shelf and make a substantial mess. 1 run out of 84 random test is a pretty good rate of success.
The result had a beautiful matt metallic finish resembling blackened steel.
After researching black sand and its use I have been able to successfully use it as an addition to my work. Temperamental, hard to control and makes a mess of kiln shelves, but to pretty not to use.