What is the pattern on this slate disk?
This thin slate disk engraved with triquetra knots is possibly from Aberglaslyn. Trial pieces were used for preliminary sketches of decorative motifs made by craftsmen who were experimenting with design and layout prior to executing them finally in metal or bronze. They may have been trying out ideas, or were patterns to show them as training guides for apprentices. It could possibly be a design for a piece of jewellery.
The triquetra, also known as the Trinity Knot, is a symbol with deep historical and cultural significance. The Celtic trquetra appeared in metal work and manuscripts around the 7th century, famously in the Book of Kells, and also on stone carvings. The symbol holds different meanings, but the power of three is a central theme. For Pagans it symbolises the three reams (land, sea, sky) in Celtic tradition the life cycle of birth, death and rebirth, and in Christianity the Father, the Son and the Holy Spirit.
This dates from the early medieval period when Christianity spread across Wales.