Complex sentence: Another experiment was conducted by Josiah Wedgwood who used it in his'Jasper ware', the mineral had previously been considered as worthless and was known as poisonous by locals, who had used it with bait to kill rats.
Split into simpler sentences: Another experiment was conducted by Josiah Wedgwood who used it in manufacturing'Jasper ware'. Witherite had previously been considered as worthless and known to be poisonous by locals who used it to kill rats.