Search

The condition of lead chromate in gelatin and agar agar medium has been studied. In presence of agar agar medium the colloid formed is stabilised by lead ions and coagulated by the excess of chromate ions. Lead chromate forms a very stable colloid in the presence of gelatin sol which could not be precipitated by excess of lead ions or chromate ions. Due to the formation of a very stable colloid in gelatin medium, well defined rings of lead chromate are not obtained in gelatin gel.

The introduction of Variamine Blue has given a new impetus to resist pilnting. The most usual methods-resists by the lead chromate and aluminium chlorate processes - are described, and new-possibilities are indicated of producing resists under red, orange, scarlet, and bordeaux diazo components.

A survey of occupational exposure to hexavalent chromium in chromate pigment production was undertaken in factories producing lead chromate (PbCrO4) and strontium chromate (SrCrO4). Sampling pre and post-shift in a factory where SrCrO4 production had just started showed the optimum strategy for biological monitoring is the measurement of urinary chromium, in urine samples taken at the end of Friday shift and pre-shift the following Monday. However, short-term uptake may be assessed under these circumstances by the increase in urinary chromium over a shift. Body burden, representing long-term chromate exposure is best assessed by measuring chromium in whole blood or pre-shift urinary chromium at the beginning of the working week. Exceptionally high levels of chromium in blood (387-4160 nmol l-1) and urine (41-1250 nmol nmol-1 creatinine) as well as skin and nasal lesions, were discovered amongst the workforce at the strontium chromate plant. These contrasted with occupationally unexposed levels of less than 20 nmol l-1 and less than 1 nmol nmol-1 creatinine, respectively, and led to the continuation of the biological monitoring programme. At the same time, improved working practices and respiratory protection equipment were introduced. A steady elimination of chromium from whole blood with a half-life of approximately 24 days was found. This elimination rate was confirmed over a 14 day period when the workforce were completely removed from exposure. The study confirms the usefulness of biological monitoring in assessing the uptake of hexavalent chromium and control of exposure.

Twenty eight moderately water-soluble to insoluble chromium (VI) compounds, such as zinc and lead chromate, industrial and laboratory synthesized pigments, and the analytical reagents strontium, barium and calcium chromate, were physicochemically characterized and studied for cytotoxicity and morphological transformation in cultured Syrian hamster embryo (SHE) cells. In vivo validation of malignancy of transformed SHE cells was performed. A high physicochemical diversity among the complex chromium pigments was revealed. The solubility of the compounds was greatly increased after incubation in a complete medium and even higher under cell culture conditions. The cytotoxic effects appeared to be due principally to extracellular solubilized chromium because the most solubilized compounds. Zn, Ca and Sr chromates, were equitoxic at about the same Cr concentration treatment and 8-fold more cytotoxic than less soluble compounds such as some Pb chromates and Ba chromate. However, certain physicochemical properties of lead chromate pigments could also influence their cytotoxic activity. All test compounds were, in a dose-dependent manner, efficient in inducing morphological transformation of SHE cells. Many of the Cr pigments, although physicochemically different, were similarly effective in transformation induction. Nevertheless, compounds among Zn and Pb chromates had various transforming potencies. Ba chromate was the least active in inducing transformation. Certain physicochemical properties could mediate the transforming activity but no particular relationship could be established between any one of the physicochemical parameters and the transforming potency. Cloned morphologically-transformed colonies of SHE cells were grown in soft agar medium and showed true neoplastic behaviour by tumour formation in syngeneic animals. These results show that various chromate pigments containing either Zn or Pb, of medium to very low aqueous solubility, induced neoplastic transformation of SHE cells.

The kinetics of chromium in the rat after a single intratracheal dose of sodium, zinc or lead 51Cr-chromate have been investigated. Sodium chromate and the less soluble zinc chromate were absorbed into the blood and this resulted in increased excretion of chromium into the urine. The insoluble lead chromate was poorly absorbed from the lungs. The more insoluble a chromate was in water, the higher its elimination via the feces. With all three chromates, absorbed chromium was retained in the spleen and the bone marrow. After the administration of sodium chromate, chromium was also retained in the liver and kidneys. On the basis of the minor resorption of lead chromate, it is concluded that chromium levels in blood and urine are not indicative of exposure to insoluble chromates via the inhalatory route. Chemicals/CAS: chromic acid, 11104-59-9; chromium, 16065-83-1, 7440-47-3; lead chromate, 11119-70-3, 1344-37-2, 7758-97-6; sodium chromate cr 51, 10039-53-9; Chromium, 7440-47-3

Lung cancer mortality among 1152 men working at three English chromate pigment factories was studied from the 1930s or 1940s until 1981. Workers at factory C were exposed only to lead chromate and experienced normal mortality (Obs/Exp deaths 7/6.45). Workers at factories A and B were exposed to both lead and zinc chromate; mortality was normal among those who had only low exposure (O/E 7/6.95). For workers with high or medium exposure lung cancer mortality was significantly raised among men remaining at least a year after entering service at factory A during 1932-54 (O/E 21/9.45) and at factory B during 1948-67 (O/E 11/2.50). At factory A, 1933-46 entrants staying only 3-11 months were not affected (O/E 6/5.04) and 1955-63 entrants also appeared unaffected (O/E 2/2.00); working conditions there improved in 1955. The hazard at factories A and B affected workers who left after one year as well as those with longer service, and latent intervals were unusually short. The results indicate that moderate or heavy exposure to zinc chromate may give rise to a severe risk of developing lung cancer, but that exposure which is relatively mild or lasts less than a year may not constitute an effective risk. The results provide no indication that lead chromate induces lung cancer in man, even under conditions conducive to lead poisoning.

Low-solubility chromates, such as lead chromate, zinc chromate and calcium chromate, which are potent carcinogens, have been examined for their solubility and clastogenic effects in a cultured Chinese hamster cell line (Don) as compared with those of potassium chromate, which is a high-solubility chromate and a weak carcinogen. Lead chromate was slightly soluble in water, Tyrode's solution, protein or amino acid solution, fetal calf serum and culture medium. Zinc chromate and calcium chromate were less soluble in serum and Tyrode's solution than in water. There were good correlations between the frequencies of chromosomal aberrations in the cells treated with the above chromates and chromium concentrations dissolved from these chromates in culture medium. When the frequency of chromosomal aberration in the cells exposed to the above chromates was compared on equal amounts of dissolved chromium concentrations in culture medium, the frequency of chromosomal aberration was the most remarkable with lead chromate, followed by zinc chromate and potassium chromate and then by calcium chromate. On the column chromatographs by gel filtration on Sephadex G-200, the chromium dissolved from all the above chromates in culture medium was present with low molecular fraction. From the above results, it was assumed that the carcinogenicity of low-solubility chromates might be related to their low solubility in body fluid.

The kinetics of chromium in the rat after a single intratracheal dose of sodium, zinc or lead 51Cr-chromate have been investigated. Sodium chromate and the less soluble zinc chromate were absorbed into the blood and this resulted in increased excretion of chromium into the urine. The insoluble lead chromate was poorly absorbed from the lungs. The more insoluble a chromate was in water, the higher its elimination via the feces. With all three chromates, absorbed chromium was retained in the spleen and the bone marrow. After the administration of sodium chromate, chromium was also retained in the liver and kidneys. On the basis of the minor resorption of lead chromate, it is concluded that chromium levels in blood and urine are not indicative of exposure to insoluble chromates via the inhalatory route. Chemicals/CAS: chromic acid, 11104-59-9; chromium, 16065-83-1, 7440-47-3; lead chromate, 11119-70-3, 1344-37-2, 7758-97-6; sodium chromate cr 51, 10039-53-9; Chromium, 7440-47-3

Etude cinetique de la precipitation de PbGO 4 dans des solutions de K 2 GO 4 et de Pb(NO 3 ) 2 . Influence de l'irradiation par une lumiere monochromatique

The «chrome yellow» compounds are solid solutions of lead chromate and sulfate. The limiting composition of the monoclinic solid solution PbCr 1-x S x O 4 corresponds to a sulphur content of about 4% i.e. 38% in PbSO 4 . The substitution of Cr by S in the lead chromate lattice results in a color change (from orange to light lemon), a decrease of the crystalline parameters and a weakening of the S-O and Cr-O bonds

It is possible to partially transform the silver chromate precipitate present in Golgi stained structures into lead chromate. When this partial replacement is followed by a treatment in a solution containing thiosulphate ions, only lead chromate is left in the tissue. This results in a depleted impregnation of the originally Golgi stained structures without fading of their borderlines. The tissue is then embedded in Araldite. Prior to ultramicrotomy, nerve cells and other structures can be identified under incident light microscopy. When studied with the electron microscope, they may reveal a relatively preserved cytoplasm within which organelles can be recognized.

n/a

This investigation is concerned with the effects of UV laser light on inorganic pigments, as extensively used in easel paintings. It has been observed that, under such laser treatment, the two iron oxide pigments raw sienna and yellow ochre darken appreciably. Examination of the X-ray diffraction (XRD) patterns of the pigments has revealed the nature of this discoloration and indicated that alterations to the structure of the crystal lattice of each pigment have taken place. These alterations are probably due to thermal processes which involve the release of molecules of water from the crystal lattice. It has been shown that, although the pigments were initially both composed primarily of the mineral goethite (FeOOH), after treatment the XRD results indicated the presence of haematite (Fe 2 O 3 ) and possibly magnetite (Fe 3 O 4 ) as well. Darkening has also been detected, following laser irradiation, of lead chromate, PbCrO 4 , a pigment that is known not to contain water. After examination by Raman and laser-induced fluorescence spectroscopy, it is proposed in this case that the observed discoloration of the pigment in the binding medium, linseed oil, is due to degradation of the binding medium or impurities therein.

To understand the reported degradation of chrome yellows, popular with artists since their introduction in the 19th century, it is necessary to understand the pigment formulation as produced at that time. Chromium-based pigments such as lead chromate (PbCrO4, chrome yellow) or zinc chromate (K2O·4ZnCrO4·3H2O, zinc yellow), as used by Van Gogh and Seurat, currently exhibit substantial darkening in paintings such as “Sunflowers” or “A Sunday on La Grande Jatte-1884”. Winsor & Newton (W&N), one of the leading artists' colourmen of the time, has made its recipe archive available. Access to their extensive chrome yellow pigment formulations prompted our research on the stability of these pigments by reconstructing their processes of manufacture. The colorants obtained were compared with contemporary tube paints from W&N as well as with samples from paintings by Amadeo de Souza-Cardoso (1887–1918) an influential modernist Portuguese painter. Good correlation between all three sources was found.

By suitable combination of vanadium pentoxide with lead chromate or elemental antimony as absorbants a simultaneous determination of sulphur and halogens in organic compounds is made possible. Substances containing nitrogen can also be analysed. Carbon dioxide does not affect the determination.

WATANABE, M., TAKAYAMA, Y., KOIKE, M. and YAMAMOTO, M. In Vivo Clastogenicity of Lead Chromate in Mice. Tohoku J. exp. Med., 1985, 146 (3), 373-374 -Cytogenetical effects of lead chromate were evaluated in vivo. When 0.5, 1, 2 and 4g/kg body weight of lead chromate suspensions in 0.5% gum arabic were administered i.p. to C57BL/6N male mice twice, the frequencies of micronucleated polychromatic erythrocytes in the femoral bone marrow were significantly (p

During theLiesegang ring formation of lead chromate in an agar agar gel it was observed that broad bands are formed in the presence of light whereas finer bands are obtained in dark. This difference in behaviour is due to the fact that lead chromate forms a more stable sol in light as compared to that in the dark.

An attempt to make use of the red color of basic lead chromate in a glaze maturing about cone 08.

Investigation of an outbreak of lead-poisoning in 121 Gurkha soldiers showed that this was due to the contamination of chilli powder (cayenne pepper), a constituent of curry powder, with lead chromate. Comprehensive systems of food sampling are needed in developing communities.

The effect of the solubility of lead iodide in the formation ofLiesegang rings has been studied. The rings are closely packed as the solubility of lead iodide is decreased. The conditions most suitable for the formation of well definedLiesegang rings of lead iodide in agar agar gel have been found out.

An investigation has been carried out into the mechanism of formation of dense precipitates from homogeneous solution by pH increase with urea.The addition of organic acids has been shown to exert a buffering action leading to the control of the otherwise rapid rise in pH, and allowing the formation of dense precipitates over pH ranges where this would not otherwise be possible. This has provided an explanation for the necessity, in many cases of precipitation from homogeneous solution, for the presence of suitable anions to produce dense precipitates.These investigations have been applied to the determination of lead by precipitation from homogeneous solution as lead chromate. A satisfactory quantitative method has been evolved, which produces easily filterable stoicheiometric precipitates.

Both the "conventional precipitation" and the precipitation from homogeneous solution are done simultaneously so that the striking differences in chemistry, appearance, and precipitate produced can be compared.

Demonstrations include the electrolysis of ZnCl2, electrodeposition of Pb, lead chromate by electrolysis, and manufacturing NaOH and Cl2 by the Hg-process.

Corrosion products are formed on the surfaces of vacuum-evaporated Au−Cr and pure Cr films on Al 2 O 3 substrates in areas exposed by the crawling back of a Pb-glass layer during the glazing of these films at 775°C. On both films red needles were observed composed of lead oxychromate, Pb 2 CrO 5 . On the Cr films, in addition, a fine orange-coloured corrosion product was formed and found to be composed of the metastable, orthorhombic version of lead chromate. On Au−Cr films the main growth direction of the needles was [020] i.e. along the b -axis of the monoclinic unit cell.

Background The first stable material used to create a gilded surface was gold. False gold was also found in the form of copper-zinc powders or silver covered with resin. There are various ways to make gold leaf adhere to a large surface area. The identification of the materials and processes to make the gilding and the use of non- invasive techniques for gilding study is still an open problem. The gilding of the medallions from the Mudejar palace of Sevilla Alcazar was investigated, and their components were characterised using non-invasive (in situ and laboratory) techniques such as X-ray fluorescence, μ-Raman, infrared spectroscopy, X-ray diffraction and scanning electron microscopy coupled with energy dispersive X-rays. Cross-sections of golden support were also performed and studied by SEM-EDX. Results The leaf adhered to the surface was primarily a gold alloy. However, copper, silver and zinc were also found. A layer of lead chromate with some lead sulphate was between the alloy and the support. This yellow pigment (lead chromate) and the layers of bole and white lead were characterised in cross-sections prepared from samples taken from the medallions in which the golden layer was missing. The support was composed of gypsum. Another golden layer applied in oldest time period was also found. Conclusion The non-invasive techniques provided useful information about the characterisation of the components of the golden medallions. However, complete characterisation of the medallions required the use of other techniques such as mass spectrometry and scanning electron microscopy- energy dispersive X-ray. This is the first time that lead chromate has been detected in gildings. The external gilding was applied at the beginning of the 19th century using mordant oil (linseed oil)., The financial support of the Spanish Commission interministerial de Ciencia y Tecnología (CICYT) under project BIA2009-12618 and the Junta de Andalucia (TEP-6558) are also acknowledged.