The trade gradually increased, until we find as many as 150 pots and kettles cast in a week.
The fuel used in the furnaces appears, from the Darby Memorandum-Book, to have been at first entirely charcoal; but the growing scarcity of wood seems to have gradually led to the use of coke, brays or small coke, and peat.

An abundance of coals existed in the neighbourhood: by rejecting those of inferior quality, and coking the others with great care, a combustible was obtained better fitted even than charcoal itself for the fusion of that particular kind of ore which is found in the coal-measures.

Thus we find Darby's most favourite charge for his furnaces to have been five baskets of coke, two of brays, and one of peat; next followed the ore, and then the limestone.

The use of charcoal was gradually given up as the art of smelting with coke and brays improved, most probably aided by the increased power of the furnace-blast, until at length we find it entirely discontinued.
The castings of Coalbrookdale gradually acquired a reputation, and the trade of Abraham Darby continued to increase until the date of his death, which occurred at Madeley Court in 1717.

His sons were too young at the time to carry on the business which he had so successfully started, and several portions of the works were sold at a serious sacrifice.