Another idea could be a series of geometric shapes and symbols inspired by Bronze Age artifacts and carvings, arranged in a stylized celtic knot pattern. The design could be printed in a metallic ink on a black or dark grey t-shirt to give it a more pronounced gothic touch. Both designs would be great examples of how Celtic style can be combined with the Gothic Bronze Age theme for an eye-catching, unique t-shirt graphic. Remember to include a vector, contour, white background, and no text to create a versatile and fashionable t-shirt design.