In response to a query about the suitability of a clay-feldspar material for use in our porcelain bodies this company asked for our "index requirements". They want to know what chemistry I want (crediting all pertinent properties to the chemistry). But physical properties like plasticity, drying performance, green strength, soluble salts are unrelated to chemistry; and fired properties like shrinkage, deformation and density are imprecisely related. Yes, Fe2O3 and TiO2 percentages do relate to whiteness and translucency for different shipments of the same material but much more poorly when comparing products from different manufacturers. The same is true of feldspars, because one has a higher flux content on a data sheet by no means indicates it will vitrify a porcelain better (it depends what minerals are delivering the fluxes and what other minerals are present).
In ceramics, glazes and bodies have a chemistry, a mineralogy and a physical presence. All of these need to be understood to adjust and fix issues.