Delft colour samples or walking stick knobs?

In the 1980s, besides tin-glazed earthenware, products that were apparently made of porcelain were found among the production waste at the sites where the Delft delftware producers Het Gecroond Porselein (1645-1753) and De Vergulde Boot (1612-1770) used to be. What is the nature of this ‘porcelain’ and how can we make sense of these archaeological artefacts?