Complex sentence: In January 1855, additional 4d stamps were needed; but when Alfred Hillman brought the stone out of storage, he found that two of the impressions were damaged, and had to redo them.
Split into simpler sentences: In January 1855, additional 4d stamps were needed. When Alfred Hillman brought the printing stone out of storage, he found that two of the impressions had been damaged, so he had to redo them.