Scars on surfaces are unsightly, especially on smooth, glossy surfaces. Surfaces can be ruined so easily - for example marks on the matte polished surface of a table by a fingernail, or on the shiny bodywork of a Cadillac by a twig. Great annoyance can result from such small causes.

Marks can also be caused by metallic objects. The culprits may be metal particles from coins, cutlery or rings on fingers. Any of these can mar surface finishes.

The scarring tool in the form of a disc, with locking facility, made of special plastic or metal, is mounted on a screw and is under pressure from a helical spring. This applies a force which is adjustable from 0 to 20 N. The instrument is placed onto the surface so that it rests on the two guide wheels and the marking wheel which is locked in position then presses onto the surface with the preset force from the spring. The range of spring forces available is divided into three sections, each covered by one of three exchangeable springs.

Test range 1: 0 - 3 N - Sensitivity: 0.1 N
Test range 2: 0 - 10 N - Sensitivity: 0.5 N
Test range 3: 0 - 20 N - Sensitivity: 1.0 N

Note: The marking discs will wear at the point at which they are used. After 100 tests the discs should therefore be moved round so as to bring a point about 2 mm further along the periphery into operation. The point at which the marking disc is first used should be marked by a scratch.

First set up the selected test wheel depending on the test required, i.e.

- the plastic disc for scar-resistance tests
- the copper disc or other special disc for metal marking

After tightening the screw it must not be possible to turn the marking disc. The spring is then set to provide what is anticipated to be a suitable force and the instrument is placed perpendicular onto the test surface and pressed down so that the guide wheels touch the surface. In this way the preset pressure of the test disc is fully effective on the test surface. The instrument is then moved a distance of a few cm so that the wheels roll over the surface in a rapid motion appropriate for the scarring effect. The test result is the minimum spring force in Newtons which will produce a clear surface scar visible with the naked eye but not a crack or scratch.

If the interest is in the so-called metal marking effect, the result is expressed in terms of the spring force at which the surface just shows a black or grey mark.