SHARPIE/MARKER PATTERNS
Applying speckles with a sharpie marker can often be a good technique for creating the speckle pattern. This technique
affects the surface minimally and allows for measurement of very high strain. It also allows for very controlled speckle size
and the ability to be applied to specimen with complex geometry and textures.
Simply dot the surface of the specimen with the marker to create dots of the desired size (several sizes are available: ultra-
fine, extra-fine, fine point, marker, and bold). A white base coat with black markers provide excellent contrast.
PRINTED PATTERNS
For medium through large surfaces, printing speckle patterns can be effective. This technique has been used with
specimens from 1” (25mm) through 12’ (4m).
Patterns can be generated using a speckle pattern generator (available for download here:
http://www.correlatedsolutions.com/installs/speckle-setup.msi
). The pattern can be adjusted in density, dot size, variation,
and field size. Print such a pattern onto vinyl appliqué or adhesive labels, making sure it adheres to the specimen well
enough to deform with the surface. Be careful of any slipping or folding that could cause measurements to not accurately
represent the behavior of the actual surface.
APPLICATION SPECIFIC TECHNIQUES
SMALL SCALE/MICROSCOPIC
In small scale applications, it becomes difficult for common methods to produce small enough patterns.
For fields down to 3mm, toner powder, carbon black, or graphite powder can be use as the speckle. The particles tend to
clump together, so working with a thin amount at a time and repeatedly applying will help reduce this possibility.
There are many ways to apply the particles, but they must involve blowing small amounts of them onto the surface. Some
methods that yield consistent patterns of good quality include a small lens blower or atomizer. Using paint or ink with an
airbrush also provides a good pattern down to around a 3mm field of view.
For patterns smaller than that, there are some other techniques such as using TEM grids as templates/stencils,
photolithography, and vapor deposition.
The pattern below was made with toner in a 2mm groove in a steel rod.
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