Richard McNemar writes in his journal that Joseph translated with two transparent stones and a hat.

The engraving being unintelligible to learned & unlearned. there is said to have been in the box with the plates two transparent stones in the form of spectacles thro which the translator looked on the engraving & afterwards put his face into a hat & the interpretation then flowed into his mind. which he uttered to the amanuensis who wrote it down, The said amanuensis by name Oliver Cowdery, was lately at the North lot & gave this account . . . there being no intelligible correspondence between the marks on the plates, & the dictates of the pretended interpreter. All his ideas were acquired by looking into a hat, where in all probability the translation appeared quite plainly in our english language. we must therefore conclude that the confabulation was cunningly devised, whether by visibles or invisibles & whether those bright & unsullied plates had been deposited in ancient or modern times.BHR Staff Commentary