The production of window glass has a long history of techniques (crown glass, cylinder glass, casted glass, …) and glass qualities (with more or less bubbles, colour, impurities,…) which did not inevitably lead to flawlessly transparent plain glass. The challenge is to understand the complexity of this evolution, which is important for both the history of material culture and the discipline of conservation-restoration. Our project proceeds from the assumption that studying glass quality solves key problems in conservation studies and the history of material culture alike, viz. 1° the bias towards conspicuous and artful objects and 2° narratives of modernity regarding the supposed shift from 'intrinsic value' to 'sign value'. Glass is a daily product without both intrinsic and (apparently) sign value and, thus, enables to assess other causal factors in the advent of modern consumer practices, such as relative prices, and technology. This requires a collaboration between historians and scholars familiar with the materiality and technicality of glass – which is available at the UADepartment of Conservation/Restoration. Methodologically, the collaboration enables to confront subjective qualities (consumer preferences) with objective qualities, such as the used ingredients and the production techniques. For the discipline of C/R this will result in more insight in the history of the choices made by both producers and consumers, and, hence, to more informed restoration practices.