P. (plaster - punic wax)
 

Plaster - 1. Shortened name for plaster of Paris which is composed of calcium sulphate hemihydrate. It is also called calcined gypsum. 2. A powder, that forms a pasty mixture with water and dries to a hard impenetrable solid. Plaster is made using several formulations. Most plasters contain calcined gypsum or lime as a binder; some contain clay. Many use sand, hair, jute or straw as extenders. Some may contain small amounts of  salts (potassium sulphate) as accelerants. Organic materials (blood, glue, casein) and weak acids (citric acid, boric acid) can act as retardants. Plaster is used as a finish material in wall and ceiling construction. In its plastic form it can be used for moulding and casting. Some examples are: 
- lime plaster - contains calcium oxide; used for frescos and wall decoration - gypsum plaster - contains calcined and ground gypsum; See gypsum cement. -  plaster of Paris - calcined gypsum; used for moulds, sculpture, casts -  stucco - contains gypsum and sand or chalk; used for walls, ceilings, decoration
Museum of Fine Arts, Boston (2000); Trench (2000)

Plaster of Paris  CaSO₄₁/₂H₂O - A fine white powder composed of calcium sulphate hemihydrate. Plaster of Paris obtained its named because it was primarily prepared from gypsum quarried in the Montmartre district of Paris. It is produced by heating gypsum, alabaster or selenite, which are composed of calcium sulphate dihydrate, to temperatures below 250°C (150° - 160°C) to drive off some of the water of crystallisation. The resulting calcium sulphate hemihydrate is stable in air, but readily combines with water to form a paste that rapidly sets (in approximately 30 minutes) to an impenetrable solid. It generates heat with setting and may expand slightly. When he set is complete the plaster returns to its original size. Setting can be accelerated by the addition a small amounts of salts (aluminium sulphate, potassium sulphate) or retarded by the addition of organic materials (blood, glue, casein). Plaster of Paris has long been used for moulds, sculpture and casts, and for the decoration of walls and ceilings. Because plaster of Paris is pure white and highly porous, the surface is readily soiled and was therefore often coated. Materials such as tea, gum arabic, waxes, shellac, lime wash and oil-based paints have been used as coatings. Plaster of Paris is also frequently painted and oil-gilded. A sealant, such as animal glue, gum arabic or shellac, is applied first to reduce the porosity of the plaster. Distemper and oil-based paints are commonly used. It is a component of alum-gypsum. 
Synonyms: calcined gypsum; burnt gypsum; partially dehydrated gypsum; plaster; calcium sulphate hemihydrate
Wittenburg (1999); Museum of Fine Arts, Boston (2000); Trench (2000)

Plaster stone - See gypsum
Museum of Fine Arts, Boston (2000)

Plasterboard - See gypsum board
Synonyms: wall board; drywall
Museum of Fine Arts, Boston (2000)

Plasterwork -  Architectural finishing or decoration executed in plaster. Plasterwork is used both internally and externally. The term stucco can also be used to describe all forms of decorative plasterwork. Renders in clay and gypsum plasters were used in ancient Egypt, India and China to produce a smooth surface over rough stone or mud brick walls. The finished surface was often painted or decorated. The Romans used mixtures of lime and sand to build up preparatory layers over which finer applications of gypsum, lime, sand and marble dust were made; pozzolanic materials were sometimes added to produce a more rapid set. Modelled stucco was employed throughout the Roman empire and plaster decoration continued to be used in Europe in the Middle Ages. From this time, surface decoration on building exteriors was produced by incising patterns into wet plaster or by moulding and free-hand modelling.  Following the fall of the Roman empire, the addition of marble dust to plaster to allow the production of fine detail and a hard, smooth finish in hand-modelled and moulded decoration was not used until the Renaissance. Stucco was widely employed by Mannerist and Baroque artists throughout Europe because it allowed the production of elaborate high relief but lightweight figurative decoration. In the 17th and 18th centuries, lime and sand mixes usually prevailed, with gypsum added to accelerate the set; if the set was too rapid to allow detailed working of the surface, glue and water were used to retard it. Various materials were used to increase pliancy, including curd, glue and almond oil. Marble dust was used where it was available. Plaster of Paris was used from the 18th century to cast repeat decoration for walls and ceilings. A further advance in the prefabrication of ornament was the invention of fibrous plasterwork in the mid-19th century, in which large sections of lightweight ornament could be quickly produced and fixed in place. Exterior stucco can be painted using the fresco technique, in which the pigments become incorporated into the plaster during the setting process, or with oil-based paints. Other surface finishes include unpainted, smooth, polished surfaces, sgraffito, scagliola, or decorations made by pressing objects such as shells, pieces of glass and mirrors, and pebbles into the plaster while wet, a technique referred to as grotto-work.
Trench (2000)

Plasterer's putty - A hydrated lime with just enough water added to make a thick paste for use as a hole or crack filler. 
RS Means Building Glossary (undated)

Plasticiser - An additive that increases the plasticity of another material, such as a a cement paste, mortar, or concrete mixture, or the flexibility or softness of organic compounds. plasticisers are usually non-volatile organic liquids or low-melting solids. Examples are dibutyl phthalate, tricresyl phosphate, ethylene glycol, and castor oil. Phthalate plasticisers were commonly used in the middle of the 20th  century for PVAC paints. However, since these oily plasticisers tended to creep and separate with time producing an oily surface and leaving a brittle substrate, later formulations began using copolymerisation techniques for film modification rather than plasticisers. 
Museum of Fine Arts, Boston (2000);  RS Means Building Glossary (undated)

Polyester resin - A thermoplastic alkyd type resin. Polyester is made by the reaction of an ester of dihydric alcohol and terephthalic acid. There are two major types of polyester. One type, polyethylene terephthalate (PET) was first developed by English chemists, J. R. Whinfield and J.T. Dickson, in 1941. PET is used to make Mylar® and other strong moisture-resistant films. The second type, polybutylene terephthalate (PBT), is mainly used as a moulding compound. When catalysed, polyesters can harden at room temperature and pressure with very little shrinkage to produce a clear, colourless fibre, block or film. 
Synonyms: Dacron® [DuPont]; Mylar® [DuPont]; Bio-Plastic; Caroplastic; Castolite; Vestopal; Terylene [ICI]; Tergal; Tetlon; Palatal; Leguval [Bayer]; Kodel® [Eastman Chemical]; Paraplex [Resinous Products and Chemicals]
Museum of Fine Arts, Boston (2000)

Polyvinyl acetate    [-CH₂CH(OOCCH₃)-]n   -   A colourless, non-toxic thermoplastic resin prepared by the polymerisation of vinyl acetate. Polyvinyl acetate (PVAC) was first produced in 1912 and was used as an artists medium in 1938. It is one of the most widely used water-dispersed resins. Polyvinyl acetate water-based emulsions have been used as latex house paints, artists' media and common household white glues. Setting is accomplished by the removal of water due to evaporation or absorption into a substrate. PVAC resins produce clear, hard films that have good weather resistance and withstand water, grease, oil and petroleum fuels. Additional properties are high initial tack, almost invisible bond line, softening at 30-45*C, good biodegradation resistance, poor resistance to creep under load and low cost. Polyvinyl acetate resins and copolymers are also used as hot-melt adhesives, sealants and plastic wood. 
Synonyms: PVAc; PVAC; PVA (incorrect); poly(vinyl acetate); vinyl emulsion; Vinamul [Vinyl Products]; AYAT[Union Carbide]; Elmers® Glue-All [Borden]; Duratite White Glue [DAP]; Gelva® [Solutia]; Rivit Glue; Resin W; Polymer Tempera [Borden]; Vinavyl
Museum of Fine Arts, Boston (2000)

Poppy-seed oil - A natural, colourless, transparent drying oil obtained from the ripe seeds of the opium poppy (Papaver somniferum) native to the western Mediterranean region. Poppy seed oil contains linoleic acid (62-72%), oleic acid (10-30%), palmitic acid (9-10%), stearic acid (1.5-2.5%) and linolenic acid (0-5%) (Serpico and White 2000). Manufactured poppy seed oil comes primarily from India, Russia, France and Asia Minor. Cold pressed poppy oil is nearly colourless, but the hot pressed oil is reddish. Poppy oil dries slower than linseed oil, but it yellows less, so it was sometimes used with white pigments starting about the 17th  century. The application of oil, including poppy-seed oil, to the surface of stucco marble has always been quite common in order to increase the gloss of an already well polished surface. 
Synonyms: poppy oil; poppyseed oil; poppy-seed oil
Wittenburg (1999); Museum of Fine Arts, Boston (2000)

Portland cement  - A form of cement originally named since it was said to be like Portland Stone in appearance. See also : cement
English Heritage (2000)

Potassium carbonate K₂CO₃  - White deliquescent powder. Potassium carbonate is used in the manufacture of glass, pottery and smalt.
Synonyms: salts of tartar, pearl ash; potash; salt of wormwood; carbonate of potassium
Museum of Fine Arts, Boston (2000)

Pozzolana -  A rosy red volcanic clay that has been used as a pigment and a component in cement. Pozzolana is mined in Italy at Pozzuoli near Naples. It is has been used since ancient times by the Romans. Pozzolana is mixed with lime to form pozzolana cement. It dries slowly but forms a strong surface. Similar cements contain trass and Santorin earth. Pozzolana was also a popular pigment for fresco paintings because it dried quickly to a hard impenetrable surface like cement. Synthetic pozzolanas are made from slag, burnt clay, HTI powder (a ceramic material ìhigh temperature insulationî), PFA (pulverised fuel ash) and powdered bricks. 
Synonyms: terra di pozzuoli; Pozzuoli red; pozzuolana; gaize cement; puzzolan cement; Santorin cement; silikat-cement; tarras cement; trass cement
Ashurst (1983)
Museum of Fine Arts, Boston (2000)

Pozzolana cement -  1. A natural cement, used in ancient times, made by grinding pozzolana with lime. 2. A cement that contains Portland cement (calcium silicate) mixed with ground pozzolana (volcanic rock) and sometimes lime. 
Pozzolana cement is a hydraulic cement that hardens with water. It is more resistant to corrosive environments than plain Portland cement. Pozzolana cement is used for wall coatings. Artificial pozzolana cement is made with furnace slag (slag cement).
Synonyms: pozzuolana cement; gaize cement; puzzolan cement; pozzolanic cement; Santorin cement; silikat-cement; tarras cement; trass cement; slag Cement
Museum of Fine Arts, Boston (2000); RS Means Building Glossary (undated)

Prussian blue  Fe₄[Fe(CN)₆]₃  -  A vivid, lightfast blue pigment. Prussian blue, synthetically produced ferric ferrocyanide, was developed in Berlin in 1704 by Diesbach. It is made by adding ferric chloride to a boiling solution of hexacyano ferrate. This forms a white intermediate, called Berlin white, that is oxidised in air to produce Prussian blue. Prussian blue has deep blue, finely divided particles that are transparent in watercolours. It has high tinting strength and is stable to light, although it will fade in strong light and turns brown in the presence of alkalis or heat. It is therefore inappropriate to use it on plaster walls.  Prussian blue was the first cheap and stable pigment to replace the costly minerals azurite and lapis lazuli. It has tremendous tinting strength and is used as a pigment in watercolour and oil paints. It is listed among the pigments used for colouring stucco marble in the nineteenth and twentieth century.
Synonyms: ferric ferrocyanide; iron blue; Turnbull's blue; Paris blue; Milori blue; Chinese blue; bronze blue; Berlin blue; American blue; Antwerp blue; steel blue; mineral blue; Hamburg blue; Pigment Blue 27; CI 77510; toning blue; gas blue; new blue; Erlanger blue; celestial blue; lacquer blue; soluble blue; oriental blue; Persian blue; potash blue; paste blue; Preussisch Blau  (Ger.); bleu de Prusse (Fr,); Berlinerblau (Ger.); azzurro di Prussia (It.); azul de Prusia (Sp.); konjo (Jap.); yang lan (Ch.)
Wittenburg (1999); Trench (2000); Museum of Fine Arts, Boston (2000)

Pumice - A pale grey, porous, volcanic stone. Pumice is composed of potassium aluminium silicate with small amounts of iron and alkalis. Its spongy texture is due to numerous cavities formed by gas bubbles that were trapped when the stone solidified. Pumice is used as an abrasive. It has also been used as a coarsening agent for texturising painted surfaces. It is mentioned as grinding stone for polishing stucco marble by repeated grinding and polishing, performed with the use of a lot of water and various grinding stones, including pumice and sandstone for the first and second grinding; serpentine, limestone, hornblende, jasper, bloodstone for dark surfaces and meerschaum for white surfaces. Today also synthetic pumice and sanding paper are used for some of the grinding and polishing steps. Pumice can also be added to lime to obtain a hydraulic set. 
Synonyms: volcanic glass
Wittenburg (1999); Trench (2000); Museum of Fine Arts, Boston (2000)

Pumicestone paper - An abrasive paper.
Museum of Fine Arts, Boston (2000)

Punic wax - A processed beeswax that was used in encaustic paintings. Punic wax was probably made by combining beeswax with soda lime to produce a waxy soap. Repeated washings in hot water removed any excess caustic. Experiments conducted in Berlin to recreate an ancient recipe, yielded flakes of a hard brittle wax that melted between 73-75*C (163-167°F) (Wehlte 1975).
Synonyms: Carthagian wax; eleodoric wax
Museum of Fine Arts, Boston (2000)
 
 
 

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