Summary. Vitreous slag‐like material, known as ‘cramp’, from prehistoric cremation burial sites in Orkney is, apart from cremated bone, one of the recurrent remains found within or around Bronze Age burials. Although the suggestion that cramp was formed by the fusing of sand attached to dry seaweed while it was being burnt was first proposed in the 1930s, there has never been a consideration of seaweed's contribution to cremation other than as a potential fuel. Scientific analyses presented in this paper corroborate the use of seaweed. It is suggested that cramp may have been deliberately produced to act as an efficient collector of shattered bone which otherwise could have been lost during the cremation. Far from being a ‘waste’, cramp could well have been another form of ‘human‐remains’ in its own right.