"Developed by Josiah Wedgwood in 1768 as Black Basaltes or black porcelaine, in order to imitate Greek vases - then thought to be Etruscan - to which he could add his patented polychrome 'encaustic' painting.
Since the idea of black stoneware was not new, Wedgwood made no attempt to patent it; but he correctly identified the best moment to develop it...Having good turning and casting properties, this adaptable material, generally known in the trade as Black Egyptian, was soon being mass-produced in Staffordshire and Yorkshire, effectively replacing the ubiquitous red teapot with a black one."
Source: Page 222 English Potter 1620-1840 by Robin Hildyard
"...The body utilised by the two earliest industrial manufacturers of the ware, Wedgwood and Humphrey Palmer, was composed of 20 each of Purbeck clay and of calcined iron to one of manganese. It was fired in an oxidizing atmosphere at stoneware temperatures (approximately 1200 degrees centigrade). Formulas for basalt frequently made use of a colouring agent called 'carr' which is an oxide derived from iron residue in the drainage system of the mines...Manganese was available from Cornwall..."
Interestingly enough black basalt tea pots became 'all-the-rage' because they showed off the beauty and grace of the hostess' hands as you'll note from this exchange.
"Wedgwood produced numerous black basalt tea pots "and in a letter to Bentley: 'Nobody makes black T.pots but Palmers". Wedgwood clearly means 'nobody else' as the firm had been producing teapots for some time Black teapots appealed to feminine vanity by enhancing the whiteness of the pourers' hands as acknowledged by Wedgwood in a letter to partner Bentley in late 1772: 'Thank you for your discovery in favour of the black Teapots. I hope white hands will continue in fashion and then we may continue to make Black Teapots'.
By mid-1774 Wedwood seemed to be satisfied with the black body he was producing, acknowledging that he was still using the same proportions mixed in the first firings six years earlier. One variable seemed to be in the surface treatment of the wares, some pieces were scoured with soap, sand and water; others left in a natural unscoured state. This undoutedly accounts for the variation in sheen seen on many Wedgwood and Bentley pieces of about this same period. In addition to the experimentaion with surface treatment, Wedgwood also investigated firing the wares at a lower temperature in the biscuit over, perhaps to alleviate the fragility and consequent breakage in transit."
Source: pgs. 27, 60, 61 of "Black Basalt Wedgwood and Contemporary Manufacturers by Diana Edwards"
Basalt is a wonderful medium. If you decide this is the kind of pottery you would like to collect or if you find your self enamoured of Wedgwood then, I would highly recommend Diana Edwards book, it is absolutely fabulous. She will walk you through the history of Basalt and all things Wedgwood. You'll truly get an understanding of the history behind the pottery and why this is a collection that just can't be ignored.