As the slag becomes enriched with iron oxide during the reaction in air, it becomes basic and then combines with the siliceous refractory lining, which is very acidic. A basic refractory lining would not react and would therefore lower the cost of production. The adoption of a lining inspired by one developed by Sidney Thomas and Percy Gilchrist in 1877 was suggested by Hollway during his last tests in the early 1800s. However, the idea was not tested, as fundamental problems related to the air blowing were more of a problem than refractory optimization.
In 1890, a basic refractory lining was tested on one of Parrot Smelter's Manhès-David converters, in Butte, under the direction of Herman A. Keller. The tests did not result in a lining compatible with industrial operation. In 1906, Ralph Baggaley, still in Montana, succeeded, after a number of tests, in industrializing a basic coating at Pittsmont Smelter, which was abandoned in 1908 after he left the factory. After all that, the Norwegian Kudsen succeeded as of 1908 in using a basic coating with the Sulitjelma Mines. He carried out two successive blowings there, initially in a small converter with a basic coating, and then in a second traditional converter with an acidic coating.
Finally, in 1909, at the Baltimore Copper Company's Smelter, the Americans William H. Peirce and Elias A.C. Smith succeeded in addressing the main drawbacks of basic refractories; basic refractories were more fragile, and, above all, they dissipated more heat than acidic refractories. By developing a masonry suitable for the cylindrical converter and increasing the amount of metal fed into the furnace, they solved the remaining problems.
Peirce and Smith's converter proved much more advantageous than that of Manhès and David. The basic refractory, which did not react with slag, lasted much longer. This improvement eliminated the need for replacement of the converters, the construction of masonry installations, and replacement converters (there were two masonry converters for every one in service in 1897 at Anaconda Copper). It also reduced the risk of piercings due to poor control of wearing of the refractory. The refractory layer could then be thinner, increasing the capacity of the converter. The capacity was not dependent on wearing of the refractory, thus simplifying the management of the flows of molten metal in factories.
If the material used to prepare the acid refractory contains copper, or even silver or gold (frequently associated with copper in gold-bearing quartz), these metals join the matte as the lining is removed. Considering the refractory's rapid destruction, the economic advantage of an acidic refractory is therefore only realized if its consumption adds value to the process. This situation is however rather rare and, even if this is the case, silica rich in precious metals can be made by other economically viable means. Therefore, in 1921, the basic refractory was considered the main factor in the cost reduction in the extraction of copper ores. In some cases, a reduction in conversion costs from $15–20 to $4–5 was reported.