As others have observed, little info. Denart is not a currently registered TM. No UK company registered solely Denart or Denart Ltd.
Two people who may be able to assist further:
Glass Association member, Dr Graham McLaren, at Bath School of Art and Design, who has written a treatise on transfer screenprinting and implementation of the technology, at Capper Ratauds Ltd,
and Shane P. O'Toole, a former litho printer at Capper Ratauds.... His contact details/info can be found using a search of name and Capper Ratauds ( employed there 1976-1988).
It is possible one or other may have knowledge of Denart. If not, K.H. Bailey and Sons Ltd, another significant manufacturer of transfers to glass and ceramics industries, are still in existence at their Dunning Street, Tunstall, S-o-T offices, and it may be that they have knowledge of Denart.
M