Plaster is the most common finishing material in the early modern interior, whether plain or decorative. There are two principal types, lime and gypsum. In northern Europe lime was widely used, made from limestone that was burned and slaked and mixed with sand, water and animal hair. In Italy, Spain and other Mediterranean countries gypsum was the primary material. Gypsum plaster was made by heating gypsum, alabaster or other forms of calcium sulphate to drive off water and form the hemihydrate commonly known as ‘Plaster of Paris’. This was then mixed with water and reverted to its full form within minutes unless retarded. An aggregate of crushed stone was used by stuccatori, in some cases of marble. By contrast, lime’s slow carbonation allowed the plasterer up to thirty days to add ornament to the surface. Thus, as lime plaster shrinks in a slow drying absorption of carbon dioxide and Plaster of Paris expands rapidly in setting, the two materials were often combined for better workability, faster set and avoidance of shrinkage. Contracts specify high quality lime and gypsum, often indicating the precise source. It is unsurprising that the most successful stuccatore in England, Francesco Vassalli, settled at Wolverhampton within easy reach of an extensive supply of Staffordshire alabaster.
In both types of plaster three coats of progressively fine plaster were applied, beginning with the ‘keying’ coat which was applied to a surface of timber laths attached to the brick or stone wall with iron ‘holdfasts’ and large plasterers nails. The fire at Clandon Park in Surrey has revealed the lath backing for the stucco scheme of the Marble Hall, together with armatures of reeds and other materials which were used for the modelling of projecting elements, while the original plaster decoration of Edward Lovett Pearce’s Stillorgan Grotto is evoked by large nails fixed to the brick structure. James Gibbs specified heart of oak laths for the plastering of the Radcliffe Camera.
Scaffolding was an essential and expensive element of the plasterer’s contract, on occasion paid for by the client but more often included in the contract. Sir William Chambers’ correspondence suggests, at least in the domestic context, that the plasterer’s scaffold was a compact structure. In June 1770 he wrote to Woburn Abbey about a pending visit: ‘… as I shall want to fix up some paper patterns in the Library Ceiling … be pleased to have 2 or 3 plaisterers trelases in the room to form a moving scaffold high enough to reach to the top of the cove…’ (BL ADD MS41133). While we know that large fixed scaffolds were employed in churches, a lighter structure is also suggested by Andrea Pozzo’s image of a plasterer at work.
Geoffrey Beard, Stucco and decorative plasterwork in Europe ( London, 1983)
Christine Casey, Making magnificence: architects, stuccatori and the eighteenth-century interior, New Haven and London, 2017
William Millar and George Bankart, Plastering plain and decorative, 4th edn. Shaftesbury, 2013
Pursche, Jürgen, ed., Stuck des 17. und 18. Jahrhunderts. Geschichte – Technik – Erhaltung, proceedings of the International ICOMOS congress, Würzburg, 4–6 December 2008 , Berlin, 2010
L.Rampazzi, B.Rizzo, C. Colombo, C. conti, M.Realini, U.Bartolucci, M.P.Colombini, A.Spiriti, and L.Facchin, ‘The stucco decorations from St Lorenzo in Laino (Como, Italy): the materials and the techniques employed by the “Magistri Comacini”’, Analytica Chimica Acta, 630, 1 (7 December 2008): 91–100