This is what was used in schools to teach children how to write
In 1778, Thomas Pennant in his book “Tours in Wales” states that 136,000 writing slates were manufactured and exported from Port Penrhyn in twelve months. Bangor in 1880 had five producers of writing slate working within the city. The best documented is perhaps the factory at Port Penrhyn, photographed by John Wickens. On the beach nearby, many remnants of writing slates can be found today. The slates were ideal for practising handwriting or drawing as mistakes could be erased.