Wytwarzanie dekoracyjno-ochronnych warstewek tlenkowych na dużych obiektach w ekspozycji zewnętrznej : na przykładzie konserwacji części metalowych Kolumny Zygmunta w Warszawie

• Autorzy: Socha Jan , Safarzyński Sławomir , Lesiak Marian

Warianty tytułu

EN

THE PRODUCTION OF DECORATIVE AND PROTECTIVE OXIDE COATINGS ON LARGE STRUCTURES IN OPEN-AIR EXPOSITIONS (EXEMPLIFIED BY THE CONSERVATION OF METAL PARTS OF THE COLUMN OF SIGISMUND IN WARSZAWA)

• Języki publikacji: PL

Abstrakty

EN

The Column o f Sigismund III Vasa, the first secular monument not only in Warsaw but in Poland, (1644), to be put up in an open-air setting, was partially damaged during the 2nd world war. In the years 1948—49, during the reconstruction o f the monument, a number o f its cleaned parts and all metal elements were covered with a decorative coating o f a sulphide type. During the last conservation o f the column in 1977 corrosion was removed from metal parts and on their surface a decorative and protective coating o f coloured oxides was produced by means o f a newly developed method. In natural conditions, in the atmosphere free from industrial gases, products o f coal combustion and pollution with substances produced by I.C. engines, a thin coloured layer, mostly made o f cupric oxide (CuO) with a possible admixture o f cupreous oxide (Cu20 ) is usually formed on bronze works. The layer, formed in a natural way as a product o f the reaction o f copper and its alloys with a surrounding atmosphere, is a coating o f decorative and protective nature. That is to say that apart from a decorative effect it markedly improves anticorrosive properties o f the surfaces o f the structures. Oxide layers on copper and its alloys can also be produced in an artificial way, chemically, in the solution o f alkalis and oxidizing agents. In general, conversional oxide coatings on copper and its alloys are produced chemically in the solution o f sodium hydroxide (NaOH) and some potassium persulphate (K2S20 8) added as an oxidizing agent. The formation o f an oxide coating on copper and its alloys in this solution takes place in two stages : — in the first stage (copper dissolution) a compound if formed which is a salt and in which the role o f acid oxide is payed by cupric oxide : S2O2-/8 + 2OH- = 2SO2-/4 + H2O + O Cu + 2OH- + O = СuO2-/2 + Н2O — in the second stage (formation o f the coating) this compound decomposes and isolates cupric oxide which crystallizes on the surface o f the object: CuO2-/2 + H2O = CuO + 2OH- The speed o f dissolving metal in the discussed solution is the highest at an initial period o f oxidation, then it gets down and after a short time acquires a constant value. The authors examined the possibility o f producing oxide coatings on large bronze constructions (monuments), displayed in open-air, through wetting their surfaces with alkaline solutions and oxidizing agents. The results obtained with these trials can be presented in the following way : The solution o f sodium hydroxide and potassium persulphate is really effective only when surfaces are damped with a hot solution. As a result o f this treatment a homogenous coating o f light brown colour and a tint o f putrid green is formed on the surface o f the object (monument). The coating, with products o f copper Dissolving included into it, formed during the creation o f an oxide layer, is bound very well with a metal o f the foundation ; still, it has no decorative expression (it does not make ,,pure” colour). An additional treatment o f brushing with a soft brush damped in a special solution for copper colouring made it possible to extract green products from the layer and give it thus a decorative look. The colour o f the coating obtained in this way may be changed depending on the number o f cycles used, varying from light to dark brown and a tint o f black. Before commencing proper conservation o f metal parts o f the Column of Sigismund III Vasa in Warszawa, the authors made a number o f chemical analyses with both metals o f the foundations o f individual parts o f the monument and o f products o f corrosion. A number o f metalographic microsections o f the superficial layer were made. Apart from deposit corrosion in a form o f relatively loose coatings, mainly o f alkaline copper sulphate, the examinations revealed also more dangerous sub-deposit corrosion (under the surface o f a conversional layer). Analyses made showed a different degree o f the corroding o f individual parts o f the monument and this resulted in a necessity o f a selective priming o f the work’s surface for conservation operations. To begin with, special pastes were used to dissolve products o f corrosion. Then, after a thorough mechanic cleaning, the surfaces were degreased carefully, activated with a mineral acid and an oxide coating was then produced in a way described herein. In the final stage all bronze elements were covered with microcrystallic wax. The oxide layer obtained in this way on the surface o f the monument is a decorative-protective coating, much more mechanically and chemically resistant than traditional sulphate coatings.

• Wydawca: Narodowy Instytut Dziedzictwa
• Czasopismo: Ochrona Zabytków
• Rocznik: 1979
• Numer: 3
• Strony: 208-220

Daty

wydano

1979

Twórcy

autor

Socha Jan

• doc. dr, Instytut Mechaniki Precyzyjnej w Warszawie

autor

Safarzyński Sławomir

• mgr, Instytut Mechaniki Precyzyjnej w Warszawie

autor

Lesiak Marian

• mgr, PP Pracownie Konserwacji Zabytków— Oddział w Warszawie

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