I tried to send you this message directly but the address failed. At Ipswich Museum we used a black tape called: Black Crepe photographic tape 25 mm wide, we bought it at BDK 26 Anson Road Martlesham Heath, IP16 0JE Tel: o1473 659 059. In the past for restoration jobs I made my own with black cotton tape sized with rabbit skin and shellac (laborious!) I hope this is of some help if you have found a better product, let us know. Dominique Rogers Conservator, (Free lance) Ipswich Museum.