Rust takes many forms, as shown in this study of a Stanley No.103. Apart from the loss of Japanning, this plane suffers from the most extreme of corrosive agents.
Sometimes rust is referred to as being stable. Stable rust is well adhered rust caused through a lifetime of exposure. This is the type of rust most often found on tools. It is associated with low relative humidity, but enough for rust to accumulate over time. The rust is more or less uniformly distributed over the entire exposed surface of the metal. Exposure to continuous moisture will lead to more degradation over time. Given long enough (years of improper care), sometimes stable rust can form a patina-like coating.
Localized rusting occurs when water remains on one spot. Flash rust is rapid rusting after exposure to high humidity (i.e. flooding) – it is usually bright orange. Flash rust often occurs on parts that have been de-rusted, only to be washed in water, and not dried properly. Fig. 3 (left) shows an example of a blade which was sprayed with water – the flash rust formed in a 6-8 hour period.
Ferric oxide can take up more volume than the metal is replaces resulting in flakes spalling from the surface. Fig.4 (left) shows a blade (from the Stanley No.102) with rust spalling on the surface. The image in Fig.4 (right) is the sole of a plane with flaking rust.
Rust which forms under a protective finish such as paint or Japanning, typically causes the finish to flake off. This often occurs in regions where there is a break in the finish, such as the heel of a plane. The examples in Fig. 5 clearly show the finish on two different planes spalling off, at the heel of the plane where the finish ends, and the transition from finish to raw metal is exposed.
Pitting is corrosion which takes the form of cavities, covering a wide area, and can be one of the most damaging forms of corrosion. Pitting is caused by a localized lack of oxygen in the metal – this causes the area to readily give up electrons to surrounding areas with more oxygen (which accept the electrons more readily), and accelerate the rusting process. The images in Fig. 6 show some extreme pitting on a block plane. The first image (left) shows pitting on the sole of the plane, and the other (right) acute pitting on the blade depth adjustment mechanism.
Susceptibility to Rust
The regions of a tool most susceptible to rust are those where moisture can become trapped. Other regions of a plane susceptible to rust are the non-finished regions of the inner body, such as where the blade is supported near the bed (Fig.7).
The image in Fig. 8 (left) shows the blade depth adjustment mechanism on a block plane – both the adjusting lever and machine screw shows signs of corrosion. Just because a knob, or lever is “plated” does not mean it is not susceptible to corrosion. The photograph in Fig. 8 (right) shows how rust has assaulted the fine [depth adjustment] grooves on the back of the blade. Small detailed crevices are often the most seriously affected regions, due to their propensity to trap moisture.
Methods of rust removal
Removing rust can be done in numerous ways, but they basically fall into two categories: abrasive or chemical . Abrasive means include the use of rust “erasers”, abrasive paper, and devices such as the Dremel “detail abrasive brush”. Chemical implies some form of liquid or gel rust remover, or electrolysis.
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