When were they made?
A number of the fireplace slates found in Dyffryn Ogwen, or which originated from the valley, are dated; all dates so far discovered range between 1823 and 1843. Others of similar style bear no date but the use of the same mixture of design motifs suggests that they were carved during the same period.
The earliest dated example, shown above, displays a confident style and exhibits many details which recur on later carved slates. It does not appear to be a tentative, simple, first effort. It is obvious, therefore, that the short time scale noted above can be extended at both ends, although not very much earlier than 1823 as the large slabs were not available in quantity until the early 1820s. It is possible that the patterned fireplaces particularly those with the simple concentric circles, were made as occasion demanded during the course of the century, as were decorative objects such as small doorstops and fans.
The tradition and the associated tools must have persisted long after 1843. It is also possible that examples from the rest of Gwynedd might be slightly later in date, as the Penrhyn Quarry antedated the development of other quarries.
The short-lived concentration of the art in the 1820s, 1830s and early 1840s coincided with the trebling of the workforce at Penrhyn Quarry. It was a boom period in the valley. New houses were built and older ones were refurbished, but eventually the rate of building levelled out.
The quarry mills and masons’ yards began to make slate fireplaces of a very different kind, beautifully and deeply carved with rosettes and columns by skilled men employed specifically for the work. Such purchased articles had a higher ‘value’ than the home-made kind. All these factors, when taken together, explain the rather sudden loss of respect for, and the destruction of much of the earlier, amateur work.