L. (lake - lime powder )

Lake - An organic pigment prepared when a dye has been precipitated on a powdered, colourless, inorganic substrate. The term derives from the Latin word lacca, used in the Middle Ages to denote both lake pigments and the Lac dye.  Because of its transparency, aluminium hydroxide is the most commonly used substrate or carrier. Barytes, barium sulphate, provides an opaque lake pigment. Other compounds used as carriers are: chalk, clay, gypsum, tin oxide, zinc oxide, white earth, and green earth. Often a mordant, such as tannic acid, lactic acid, or sodium phosphate, is used to fix the dye to the substrate. Many of the natural dyes were made into lake pigments, such as cochineal, kermes, madder and lac for use in oil painting. In the late 19th century the chemical industry discovered synthetic equivalents of madder and indigo and went on to produce a range of new ones from coal tar derivatives. These and many of the bright new pigments introduced in the 20th century have all been manufactured as lakes. Some, such as aniline dyes, are also prepared in this manner for use as paint pigments. See also : dye.
Synonyms: Lakes
Museum of Fine Arts, Boston (2000); Trench (2000)

Lampblack - Amorphous carbon particles obtained from the soot of burned fats, oils or resins. Lampblack is soft bluish-black pigment that is very stable and unaffected by light, acids and alkalis. The powder is extremely fine. It is a useful pigment if a very dense, opaque black is required. It was often mixed with lead white to produce a grey pigment. Lampblack may contain a small percentage of residual fats, oils or resins. This makes it mix poorly with water and also makes linseed oil dry slowly into a soft film. Umber was often added to the mixture as a drier. For use as a watercolour, lampblack was mixed with glue, prepared in sticks and sold as India ink. Currently lampblack is used as a black pigment in cements. It is listed among the pigments and dyes used for colouring stucco marble in the seventeenth an eighteenth century. See also bone black, charcoal black, and vine black.
Synonyms: carbon black; CI 77266; Pigment Black 6; smoke black; soot black; oil black; flame black; blacking; lamp black
Wittenburg (1999); Museum of Fine Arts, Boston (2000); Trench (2000)

Land plaster - An obsolete name for gypsum.
Museum of Fine Arts, Boston (2000)

Lapis lazuli  (Na,Ca)₄(Al,SiO₄)₃(SO₄,S,Cl)  -   A brilliant, opaque, azure-blue colour gemstone, with a hardness on the Mhos scale of 5.5. Lapis lazuli is a mixture of minerals, primarily containing the lazurite (blue) with small amounts of calcite, sodalite, and gold-coloured flecks of pyrite. Lazurite is a sodium, calcium, aluminium sulpho-chlorosilicate. The blue coloration, which can be deep or pale, greenish or nearly purple, is produced by sulphur contained in the lazurite. Lapis lazuli has been commercially mined since 3000 BCE at the Badakhshan mines in Afghanistan. Other mines are found in Argentina, Siberia, Chile, Myanmar (formerly Burma), Pakistan and California. The semiprecious blue stone was, and still is, used for jewellery, mosaics and small carvings. Lapis lazuli was also ground and purified to make natural ultramarine blue pigments.
Synonyms: lazurite; lapis; Persian blue; Fra Angelico Blue; Armenian stone; ultramarine blue (pigment)
Museum of Fine Arts, Boston (2000); Trench (2000)

Lath  -  Narrow strips of wood which can form the groundwork for slates, panels or plaster work 
English Heritage (2000)

Lead linoleate  Pb(C1₈H₃₁O₂)₂ - A yellowish-white paste that is prepared by heating a solution of lead nitrate with sodium linoleate. Lead linoleate is use as a drier in oil paints and varnishes to speed the polymerisation and oxidation processes.
Synonyms: lead plaster
Museum of Fine Arts, Boston (2000)

Lead plaster - A sealant composed of a fatty acid lead salt. See lead linoleate.
Museum of Fine Arts, Boston (2000)

Lead white - A white synthetic pigment (lead carbonate) made by exposing strips of metallic lead to acidic vapours and carbon dioxide. It has been an enormously significant pigment since pre-classical times. Unlike any other pigment, it forms a chemical link with the drying oil, giving the paint properties that cannot be reproduced using the modern whites titanium white and zinc white. In domestic house paint it has always been admired for the way it becomes soft and silvery with age. 
Trench (2000)

Lead white, sublimed - In current usage, sublimed lead white refers to basic lead sulphate. However, in the 19th century sublimed lead white was introduced as a non-toxic white paint pigment that contained a mixture of lead sulphate, lead monoxide and zinc oxide. Sometimes the mixture also contained barium sulphate and chalk. The mixture was also called leaded zinc white.  See basic lead sulphate.
Synonyms: basic lead sulphate; leaded zinc white
Museum of Fine Arts, Boston (2000)

Lime CaO - Any of several forms of calcium oxide obtained from heating calcium carbonate (limestone, marble, chalk and shells) in a kiln. Also, a general term for the various chemical and physical forms of quicklime, hydrated lime, and hydraulic hydrated lime. Lime is used as a constituent of modern mortar, cement and stucco or as slaked (non-hydraulic) lime in lime putty, daub, limewash and traditional lime plaster, mortar and renders. When calcium carbonate is heated to between 900°C and 1200°C, carbon dioxide (and any water) is driven off leaving anhydrous calcium oxide or quicklime, sometimes described as unslaked lime or, misleadingly, as lump lime. When quicklime is soaked in water, it is changed to calcium hydroxide or slaked lime. Slaked lime that is dried and ground to a fine powder is called hydrated lime or lime hydrate. The addition of highly reactive forms of silica and alumina, such as volcanic earths, ash or rock (such as tuff or pumice), brick dust, or ground iron slags, produces a hydraulic set in which the lime does not set by carbonation, but instead forms calcium silicates and aluminates by reaction with these additives and can solidify rapidly even under water. Materials which induce this effect are called pozzolanic additives. Hydraulic lime can also be made by calcining limestones such as lias, which have a high silica content. Lime is one of the main components of lime plaster, limewash (whitewash), marmorino and stucco lustro.
Synonyms: calcium oxide; calcium hydroxide; calcia; quicklime; caustic lime; hot lime; hydraulic lime; hydrated lime; burnt lime.
Ashurst (1983); Trench (2000);  Museum of Fine Arts, Boston (2000);  RS Means Building Glossary (undated); English Heritage (2000)

Lime, air-slaked - A white powder containing both calcium carbonate and calcium hydroxide. Air-slaked lime is lime that has absorbed carbon dioxide and moisture from the atmosphere. 
Synonyms : wind-slaked lime.
Ashurst (1983)
Museum of Fine Arts, Boston (2000)

Lime, wind-slaked - A white powder containing both calcium carbonate and calcium hydroxide. Air-slaked lime is lime that has absorbed carbon dioxide and moisture from the atmosphere. 
Synonyms : lime, air-slaked.
Ashurst (1983); Museum of Fine Arts, Boston (2000)

Lime ash  - The residue from the kiln floor of lime-burning in the traditional manner firing coal and/or wood and lime together in a clamp or kiln. Mixed with water and plasticising or setting additives and reinforced with reeds and straw it formed a useful flooring material or, gauged with gypsum, a backing coat for internal or external renderings.
Ashurst (1983)

Lime-and-cement mortar - A lime, cement, and sand mortar used in masonry and cement plaster. In addition to imparting a favorable consistency to the mix, the lime also  increases the flexibility of the dried mix, thus limiting cracks and minimizing  water penetration. 
RS Means Building Glossary (undated)

Lime-casein    -  A paint binder or adhesive prepared by hydrolysing casein with lime (calcium oxide). Lime-casein is prepared by soaking casein powder in water with lime. This forms a clear, viscous solution that dries to form a water-insoluble film. Lime-casein has a high pH (9.0-9.9) compared to ammonium casein (8.0-9.0), and borax casein (7.0-7.8). Lime-casein is often used as a ground or size for wall paintings on lime plaster, gypsum plaster and stone. It dries to a brittle, insoluble, matte film. Occasionally a plasticizer, such as glycerol or sorbitol and a preservative, such as phenol, are added to the solution. Lime-casein is also used as a paint binder. Because of its alkalinity, however, its pigment palette is limited (see fresco pigments).
Synonyms: lime casein; casein adhesive; casein glue
Museum of Fine Arts, Boston (2000)

Lime concrete - A lime, sand, gravel, and concrete mix made without Portland cement.  Lime concrete is found in older structures, but is no longer in general use. 
RS Means Building Glossary (undated)

Lime flour -Finely powdered lime.
Museum of Fine Arts, Boston (2000)

Lime hydrate - Lime, calcium oxide, that has been slaked, or hydrated, to form calcium hydroxide. then dried and ground to a fine powder. See lime.
Museum of Fine Arts, Boston (2000)

Lime mortar - A masonry mortar that is composed of hydrated lime or lime putty and water with sand or marble dust. Lime mortar was the primary mortar used for masonry before the invention of Portland cement  (Bucher 1996). Nowadays it is not often used because it hardens at a very slow rate. It has been used as a plaster for fresco (Mayer 1969).
Synonyms: lime-sand mortar
Museum of Fine Arts, Boston (2000);  RS Means Building Glossary (undated); Bucher (1996); Mayer (1969).

Lime plaster - A type of plaster composed of calcium oxide (lime). Lime plaster has been used since antiquity. It is prepared by heating limestone to high temperatures over a long period to remove the chemically bound water, thus producing calcium oxide (quicklime). When quicklime is mixed with water, it converts to calcium hydroxide (slaked lime). Slaked lime hardens by the evaporation of water. The set of lime is very slow and requires the presence of carbon dioxide. Also, without additives the plaster is weak and prone to shrinkage and cracking.  Often aggregates or binders are added to increase the strength and decrease porosity. Lime plasters were used for wall coverings, frescos and wall decoration. For wall plaster, animal hair gives the lime and sand greater toughness and cohesion; in medieval work gypsum plaster was frequently added to lime as an accelerator of set. Additives to provide water-repellency, such as tallow or linseed oil, or to entrap air and thus improve the set, such as urine or beer, were traditionally used. For hand-modelled ornament gypsum was added, with a retardant such as glue, sour milk or wine, to allow a long working time. Marble powder was added as an aggregate because it permitted the rendering of fine detail. Lime plasters were commonly used in Europe, both internally and externally, but their long setting time of several months made decoration with paint or wallpaper difficult. 
Synonyms: lime; quicklime; slaked lime
Trench (2000); Museum of Fine Arts, Boston (2000)

Lime powder - A 19th century name for air slaked lime.
Museum of Fine Arts, Boston (2000)
 
 

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