there is a gorgeous rummer showing in Timothy Mills book 'Rummers - A Social History Told In Glass' showing an example of his invention - pp. 48/49 - and detailing the method of Davenport's method of decorating glass. In precis it was to do with covering the glass object in a glass paste - this was then scraped away to leave the desired pattern, then fired to fix the design. Seems to have been too costly and time consuming to be commercially viable. Assume m, that you do of course have a copy of Tim's book.