THE RUDOLF REPORT

GERMAR RUDOLF · THE RUDOLF REPORTwas tested during an environmental resistance test lasting 21 years inthe industrial district of Slough, west of London. 381 In so doing, piecesof aluminium sheet metal were alternatively dipped in an iron(III)-cyanide and then in an iron(III)-salt solution, 382 by which the resultingpigment was adsorbed on the aluminium sheet metal. The test sheetswere then exposed to the environment on the roof of a building in avertical 45° angle facing south-west.During the 21 years lasting test, in which eight Iron Blue sampleswere tested among other pigments, the Iron Blue, in particular, followedby iron ochre (Fe 2 O 3 , rust), exhibited only minimal alterationsafter this period of time. One sample of Iron Blue and iron ochre wasremoved only after 10 to 11 years in each case. 383 All other samplesstill exhibited an intense blue color. Half of the seven remaining IronBlue samples received the value 4 out of a maximum of 5 points forthe best retention of quality, on the grey scale used there in the determinationof color changes. Only minor alterations were detected.The exhibits were therefore exposed to the environmental conditionsof a strongly industrialized area, with full effects of precipitation,direct sunshine, and wind erosion for more than 21 years. Under intensesummer sunshine and in the absence of wind, the temperature ofthe dark-blue colored aluminium metal sheets rose steeply (Iron Blue isonly stable up to approximately 140°C. 384 ). Snow, frost, hail, storms,and the finest, driving acid drizzle had obviously just as little an effecton the pigment as the UV radiation of direct sunlight. What is remarkableis that in determining the degree of destruction of the pigment nounexposed samples were used since these had been lost over the 21-year period; rather, places on the surface of the exhibits which hadbeen relatively well protected from direct environmental influences bythe frames and by rubber rings on the screw joints were used as controlsamples. These exhibited almost no alterations.In comparison to the environmental conditions which are of inter-381 J.M. Kape, E.C. Mills, Tranp. Inst. Met. Finish., 35 (1958), pp. 353-384; ibid., 59 (1981), pp.35-39.382 K 4 [Fe(CN) 6 ] 3 or Fe(NO 3 ) 3 .383 The literature does not, however, mention this Iron Blue sample as “Prussian Blue”, like theothers, since it was, at that time, considered to be of another type, i.e., “Turnbull’s Blue” or“ferrous ferricyanide”.384 Compare Ferch, H. Schäfer, op. cit. (note 333); S. Barbezat, J. Réch. Cent. Nat. Réch. Sci. 4(1952), pp. 184ff.; E. Gratzfeld, Färg och Lack, 3 (1957), pp. 85-108; E. Herrmann, Farbeund Lack, 64 (1958), pp. 130-135.178