The archives were Ianto's domain.
He knew where everything was kept, and more to the point where he kept things hidden from Jack.
In a rarely used corner of vault 78 was a large crate marked sbwriel saithdegau.
Jack refused to learn Welsh so he had no inclination to look inside the crate.
Object in hand, Ianto prised open the crate and updated the register of contents. Four disco balls, twelve Beegees records, fourteen pairs of bell bottom pants, six pairs of men's platform shoes, a light up dance floor, and now six lava lamps.
Jack's seventies obsession ended here.
A/N - apologies for the translation. My Welsh is awful!