Each Multi-Finger Scratch / Mar Tester includes a set of five 1.0mm diameter hemisphere Scratch Tips and 7.0mm diameter hemisphere Mar Tips.  Both include a precision tungsten carbide ball mounted to the contact end.  Optional conical scratch tips are also available in either tungsten carbide (0.1mm; 0.25mm; 0.4mm and 0.5mm diameter) or diamond (with 90° 3mil or 90° 3.5mil radius point).

Depending on the type of material under evaluation, the visual appearance of a scratch normally involves changes in surface topography, color, or brightness.  Three methods are normally used:

Visual Evaluation – For this technique, the observer uses a controlled light source to visually inspect each scratch line and rates according to a Rating Scale 1 to 5 (1 = no scratch line at all; 5 = severe scratch line).  For plastic materials, indicate if the line exhibits signs of whitening.

Width/Depth – Using an optical measuring device such as an Optical Micrometer, the operator measures the width and / or depth of the scratch.

Image Analysis – Another option would be to use an Image Analysis technique such as SEM.

Detailed descriptions are recommended when depicting scratch or mar damage.  Items that might be described include surface topography, material deformation, material removal, and color changes.  The following examples have been used to describe damage in plastics:

• scratch is shallow (or deep)
• scratch is smooth, with a well defined shape (or rough and deformed)
• scratch includes plastic flow of the material (or cutting, tearing, cracking, chipping, crazing)
• scratch includes visible ripple marks at the bottom (i.e. chevron or parabolic shaped)
• strain whitening is visible (or no change in color)

NOTE: The properties of plastic materials can greatly influence the evaluation of scratch and mar resistance. It is important to be aware of the following factors and take them into consideration.  For reproducible results, define if evaluation should occur immediately following the scratch test or after a specified amount of time (e.g. 24 hours).

• Many plastics have elastic recovery upon removal of applied stress.
• Many plastics have visco-elastic properties and the stresses in the plastics may relax during loading.
• Plastics may change structure during material flow, which can also change the mechanical properties of plastics.

The following link provides a listing of test methods the Taber Multi-Finger Scratch / Mar Tester satisfies.  Please note, additional accessories may be required.