Conservation of Historic Metals by Waterjetting Techniques

Abstract

Water cleaning has long been used in the conservation of historic metal artefacts and structures and has been fairly well documented in the conservation literature. Typically, low and medium pressure (not exceeding 4,000 psig) water cleaning techniques such as nebulous mist, steam, and power washing have been used to assist the conservator in implementing conservation treatments, not only because they are safe and effective, but also because conservators are not usually fully versed in the principles and technology behind high and ultra-high pressure waterjetting. High to ultra-high pressure (4,000 psig to 50,000 psig) waterjetting is a specialized technique that has been utilized in the commercial cleaning and surface preparation industry for years but has only been used in the conservation field on a handful of projects. In addition to low and medium pressure cleaning techniques, the authors have used high and ultra-high pressure water cleaning techniques extensively on historic metal artefacts for the removal of coatings, corrosion products and soluble salts while making it possible to preserve desirable original coatings and patina materials.In metal conservation there exists a delicate balance between the goals of the conservation treatment including surface preparation, with its technical aspects of surface profile or roughness, visible cleanliness, and non-visible cleanliness, and ethical issues of minimal intervention and maximum preservation of original material. Since the late 1980s, conservators have studied the effects of medium and high (not exceeding 35,000 psig) water pressures on bronze monuments in an attempt to replace abrasive blasting techniques to remove unwanted corrosion products while still retaining the aesthetically desirable patina layers. Since then, the authors have performed testing and implemented treatments on steel and aluminium historic artefacts using high and ultra-high waterjetting techniques.This article will provide a practical introduction to waterjetting technology with specific cases of its use in the conservation of metals. A brief recounting of the application of low to medium pressure waterjetting techniques used by outdoor sculpture conservators will be provided, followed by recent applications of high and ultra-high pressure waterjetting in the conservation of the ‘Big Piece’, a salvaged steel hull section from the Royal Mail Ship (R.M.S.) Titanicwreck-site and for the conservation of two Saturn V rockets on display at Johnson Space Center in Houston, Texas and the United States Space & Rocket Center in Huntsville, Alabama.