Artist Appendix Medieval Materials
Artist Appendix for Banner of Ghent.
The pigments considered are whites (leadwhite, titanium and calcium carbonate), yellows (ochres, lead tin yellows), orange-reds (ochres, red lakes, vermillion), blues (smalt, woad), greens (green earths, copper salts and other Cu containing materials), brown (umbers) and black (carbon black and black dyes). While no specific modern chemical analysis on the Banner of Ghent has been published, reasonable materials and methods used in the Netherlands during the same period (and in other paintings/illuminated manuscripts of the same era) are considered.
Alum Potassium aluminum sulfate is the mordant most frequently used by dyers for protein (animal) and cellulose (plant) fibers and fabrics. It improves light and washfastness of all natural dyes and keeps colors clear. It is inexpensive and safe to use. A historian form of alum is refined from bauxite, a native reddish mineral found in Europe.
“Redoul” Dye involving barwood of redoul will react with copperas and give darker grey and logwood, with a little brazil wood for some nuances, to black colours. PFAF.org: Black dye: A black dye and an ink is obtained from the leaves[11, 103]. The bark can also be used, both the bark and the leaves are rich in tannin[. Blackberry bush grown in Belgium / Netherlands Candidatus Phytoplasma rubi
(Z = 20) Alba Albula, buC white colored chalk, from Albula, Switzerland.
Calcium containing pigments are of mineral, biogenic, fossil or artificial origin, mainly corresponding to groups of carbonates, sulphates, phosphates, or fluorides. A variety of Ca, CaMg carbonates, and sulphates was used as white pigment (chalk, bianco di San Giovanni: CaCO3; huntite: CaMg3(CO3)4 and dolomite: CaMg(CO3)2; gypsum: CaSO4·2H2O), as well as mixed with glue to prepare ground layers in northern and southern Europe, respectively] and to prepare parchment for manuscripts. The calcination of bones gives a white pigment mainly containing apatite Ca3(PO4)2.
Calcium compounds were as well used as extenders (for example with leadwhite, to achieve transparency effects), and for lakes, as chemical or physical supports .
Extenders such as chalk, which is colorless when mixed with an oil binder, can change the working properties and translucency of the paint and can also decrease the amount of pigment required. See M. Stols-Witlox, "The Heaviest and the Whitest": Lead White Quality in North Western European Documentary Sources, 1400–1900' in M. Spring, ed., 'Studying Old Masters”
Copper Salts: “Salt Green”
In addition to malachite and azurite, a number of copper salts and related compounds are found within copper mineralization and with the corrosion of copper and bronze metals. These are attractively and brightly colored in hues of blue and green and would have been noticeable in the landscape and forming on the surfaces of metal artifacts exposed to the elements. The name viride salsum, “salt green” was coined by the 12th Century author Theophilus and has a generic application to (synthetic) copper salts.
Generally prepared from one of two closely related clay minerals, celadonite and glauconite.Perhaps the most striking feature is the extensive use of green earth in the depiction of flesh tones. Green earth was frequently employed in the 'Trecento' (the fourteenth century) as an underpaint for flesh.
(also known as yellow ocher, or yellow earth) Known since the antiquity, iron oxide earth pigments occur naturally as yellow (goethite) or as red (hematite) earths. Yellow earths have been used as a pigment since prehistoric times and is perhaps the most widely used pigment for artists paints. Depending upon the content of hydrated iron oxide, the color of ocher varies from light yellow to orange-red
Prepared by the precipitation or adsorption of an organic dyestuff onto an insoluble substrate. A common source for yellow dyestuff was the weld plant. The simplest and most direct method used to extract the dyestuff from the raw material was with water or an alkali. The alkali, or lye, was commonly prepared from the ash of wood or other plants extracted with water. The soluble dyestuff components were then converted into the insoluble lake pigment by the addition of alum (potassium aluminium sulphate) and often in the case of yellow lakes, some form of calcium carbonate such as chalk
Lake made of Reseda and Buckthorn Berries, yellow lake pigment, dark golden color more lightfast than lake from weld.
Pigment White Described by Cennino Cennini. Bianco San Giovanni, 'white pigment.' The dense, opaque white pigment, basic lead carbonate, has been produced artificially since antiquity. Stols-Witlox, '"The Heaviest and the Whitest": Lead White Quality in North Western European Documentary Sources, 1400–1900' in M. Spring, ed.
(Thin layers of metal or layers of powdered silver). Besides silver signals, XRF used in manuscripts of the time revealed the presence of titanium, i.e., titanium white (TiO2)**. The lack of any micro-Raman signals from this compound, which is a strong Raman scatterer, suggests that titanium white was used to mask the underlying picture prior to the laying of silver powder which was presently darkened by weathering.- Eleonora Pellizzi. On the Hierarchical Use of Colourants in a 15th Century Book of Hours Laboratoire Scientifique et Technique du Département de la Conservation, Bibliothèque Nationale de France, 14 Avenue Gutenberg, 77607 Bussy Saint-Georges, France
Silver leaf binders: metallic leaves could be applied over the parchment surface, previously burnished, or over a ground layer. In the cases that were analysed, the grounds were prepared with gypsum, calcium carbonate or a mixture of both, combined with proteinaceous (like egg glair or animal glue) or polysaccharide (ie starch) binders.
Silver oxidizes: silver leaf interfaces with air As S is formed possibly as a result of a soluble salt dissolution… tannins used in black dyes (also soda ash as a mordant is a salt) could reasonably contributed to the degradation of the silver leaf on Ghent’s banner. -“Silver paints in medieval manuscripts: a first molecular survey into their degradation” Heritage Science VL - 6 May 2019. DO - 10.1186/s40494-018-0172-7
Van den Berg, K.J. “A quick assessment of the photocatalytic activity of TiO2 pigments — From lab to conservation studio” Microchemical Journal Volume 126, May 2016, Pages 162-171 Titanium dioxide is a known photocatalyst. When titanium dioxide absorbs UV light a chain of events possibly leading to the production of radicals is initiated. These radicals can attack the surroundings of the pigment and that can cause a breakdown of the organic medium resulting in embrittlement, (loss of gloss or chalking.) When colorants, pigments or dyestuffs are involved, the color can also be affected and yellow.
The use of another binder, heat-bodied walnut oil, in 'Young Woman standing at a Virginal' was also confirmed by analysis. This was identified in a sample of white paint from an area of thick impasto, depicting the light entering the window at the upper left edge of the painting. Walnut oil was considered to yellow less during ageing, and was therefore traditionally recommended for use with pigments whose colour was particularly affected by yellowing of the medium, such as whites and blues.
Bole was first applied to the substrate for gilding. Despite its name, Armenian bole (bolum armenum), a red earth of pinkish colour, was found throughout Europe. Usually mixed with gypsum, it provided a firm ground for thin gold leaf. Although there is good reason to speculate the bole used in the Banner of Ghent contains caulk or titanium, it is possible it is traditional bole. Illuminators often applied several layers of bole to create the illusion of thick gold and enhance the three-dimensional effect of their images. The metal could be applied directly to the bare parchment with an adhesive — egg glair or glue made from fish or animals.-Fitzwilliam Museum: lluminated Manuscripts in the making: Painting with Metal Artist Scientific Techniques
Vermilion or Kermes
A red mercuric sulphide pigment prepared from finely ground mineral cinnabar; also in dyes cost up to 29 times as much as matter in Flanders. Species of shield-lice a parasite on evergreen oak trees. Females collecting just before laying eggs were killed and dried (kermis means small worm in Arabic) produces brilliant dyes. The source of the red organic dyestuffs could be plant or animal in origin; dyestuff could be extracted from the roots of the madder plant, for example, or from scale insects such as cochineal. Madder madder will grow in calcium-rich soils and, indeed, it has been observed that the color of textile dyeings obtained is redder if the plant has been grown on calcareous soils. Madder also prefers a moist soil, rich in organic matter, with a reasonable phosphorus content.
A red lake pigment was employed for mixed purples (with natural ultramarine).This pigment was also mixed with lead white for shades of pink,alum, generally potash alum, potassium aluminium sulphate, AlK(SO4)2·12H2O. The use of alum as a mordant in textile dyeing is well known; in the case of lake pigments, it was used as a reagent to form a substrate for the dyestuff, to make a pigment. The reaction between this and an alkali forms a type of hydrated alumina which precipitates together with the dyestuff, in solution with one or other of the reagents. The alkali was commonly lye prepared from wood ash, but it could equally well be made from lime, or varieties of calcium carbonate, such as chalk, marble dust, egg shells or cuttlefish bone could have been used. These last are more usually found in recipes for yellow lake pigments, but also occur in recipes for red or rose-pink lake pigments from brazilwood, Caesalpinia.
Brazilwood lakes were also prepared by direct extraction of the dyestuff from the wood following a variety of recipes. Often calcium carbonate (commonly chalk) was an ingredient, thus in these cases calcium-containing salts would be present. Depending on the acidity or alkalinity of the reagents used, colours varying from yellowish to purple can easily be produced, explaining the wide range of recipes available for brazilwood inks and pigments. However, it has become clear that because of the dye’s tendency to turn brown in alkaline solutions when left to stand, some pigments made by the addition of alum to an alkaline brazilwood dyestuff solution tend to be a brownish crimson colour. Alkalinity may affect the permanence, as well.- J. Kirby, M. Spring and C. Higgitt, 'The Technology of Red Lake Pigment Manufacture: Study of the Dyestuff Substrate' in 'National Gallery Technical Bulletin', vol. 26 (2005), pp. 71–87.
Known in historic technical literature as zinc vitrol, zinc was probably added to secondary ground layers needed to build up flesh tones and complex representation of fabrics since it was thought to speed up drying.
Costaras: describes methods to speed up the drying of priming layers, suggesting a number of siccatives including lithage, minium, smalt (cobalt in smalt acts as a drier), varnish and earth colours (umber contains manganese dioxide and functions as a catalyst to drying)- N. Costaras, 'A Study of the Materials and Techniques of Johannes Vermeer', in I. Gaskell and M. Jonker, eds, 'Vermeer Studies', New Haven and London 1998, pp. 145–67.
Bone black and charcoal black in a linseed oil binder.
Black Dye (Linen Ground of Banner)
Walnut (Eastern Black Walnut) Juglans nigra. This dyestuff is obtained from the bark of the tree and also from the green husks of the fruit. Domonique Cardon has called walnuts “great living laboratories of dye production.” Walnut is a substantive dye and can be used without a mordant. It can be used alone to produce warm deep taupes or to give extra depth in combination with other dyes. Also in use were peach pits, treated in a similar way.-CARDON, Dominique, and Anthony PINTO. “LE REDOUL, HERBE DES TANNEURS ET DES TEINTURIERS. COLLECTE, COMMERCIALISATION ET UTILISATIONS D’UNE PLANTE SAUVAGE DANS L’ESPACE MÉRIDIONAL (XII -XV SIÈCLES).” Médiévales, no. 53, 2007, pp. 51–63. JSTOR, http://www.jstor.org/stable/43027365. Accessed 2 Feb. 2023.
Tannins are used to assist the mordants of cellulose fibers and fabrics. Alum does not bond with cellulose fibers as well as it does with protein fibers. However, tannin bonds well with cellulose. and once treated with tannin, alum will combine with the tannin fibre complex. Many dyestuffs contain tannin (black oak, walnut, pomegranate, cutch, fustic, etc) and do not need an additional tannin.
Woad is the common name of Isatis tinctoria. In Medieval Europe it was the only native source of blue dye for textiles. The leaves of the woad plant contain the same dye molecule as Indigofera tinctoria, although in much weaker concentration. It was common to use a dark blue dye bath as the initial vat dye, and then "over dye" the same linen fabric in a second or third dye bath (such as walnut) to achieve a dark, rich hue of black.