The micro cutting-edge of geological sampling
The Geoscience Precision Cutting Facility within the School of Geography, Earth and Environmental Sciences specialises in precisely oriented micro-cuts through geological materials.
The facility is designed for single cuts through valuable or unique materials as well as making serial wafered sections. In both cases preparation attains minimal sample loss by using the thinnest saw blades available, and results in minimal damage to delicate specimens.
The available equipment is routinely used for preparation of vertebrate and palaeobotanical research specimens but is also suitable for other applications in geosciences including serial sectioning of palaeontological, petrological and mineralogical specimens.
Equipment within the lab compliments other facilities available within the School of Geography, Earth and Environmental Sciences including the Rock Sectioning suite, micro-milling facilities within the Stable-Isotope and Luminescence Laboratory (SILLA) and dedicated observation facilities including research quality microscopy and image acquisition systems.
Available equipment includes:
Buehler Low Speed Saw
Buehler Isomet Low Speed saws for precision sectioning: These are the work horses of the laboratory and are used for precision cutting of important materials in which retrieval of information and gugh frequency and precision thin cuts are paramount.
The lab uses two of these with either 4" or 5" diamond wafering blades with a minimum thickness of 0.3 mm to give minimal loss of material in sectioning. A variety of chucks are available for holding and orientating specimens including a goniometer.
Low saw speeds of 1-300 rpm ensures minimal deformation of cut specimens, and provides a smooth and blemish free cut surface that requires minimal subsequent preparation prior to observation.
Buehler 5000 Automated Linear Precision Saw
Buehler Isomet 5000 Automated Linear Precision Saw: This is the big brother of the Low Speed Saws and is used to quickly obtain precisely spaced multiple parallel cuts. It has a built in micrometer for 1-2 µm sample positioning, and a SMARTCUT system to prevent sample and machine damage. It takes up to 8" blades and has a variable speed from 200-5000 rpm.
The most impressive part of the system is that it can be set to automatically make multiple precision cuts from a single sample, with the mechanisms moving the sample in relation to the blade with great accuracy. This has proven itself to be excellent at making serial sections of a given thickness from a single sample with known spaces between sections, and fully integrating with Serial Section Reconstruction systems.
The Buehler MetaServ is a grinder/polisher that can be used on any kind of cut section. It is regularly used to grind specimens to reveal another plane below that exposed by the original cut, and is also used to polish wafered sections prior to mounting on microscope slides.
Once sections have been cut, the Buehler PetroThin can be used to grind them down to thicknesses suitable for geological thin sections for transmitted optical microscopy. The Petro-Thin is frequently used for rock sectioning.
Specimen preparation, resin impregnation and alignment
Specimens can either be cut as they occur, but in many cases specimens are embedded in resin prior to cutting. This allows reinforcement of delicate specimens and can allow a better grip of specimens with irregular outlines in the specimen holding clamps. For different materials either low or high viscosity resin is used, with vacuum impregnation used to exclude air from the preparation.
Facilities in the precision geosciences cutting suite are routinely used for preparing specimens for the purpose of constructing digital 3-D reconstructions of fossils. Details of preparation and cutting vary for individual specimens but with distances between successive parallel wafers typically varying from 0.3-1 mm, and using either 0.3 or 0.63 mm thick blades. These known blade and wafer thicknesses enable accurate reconstructions to be constructed.
For specimens that are being sectioned in order to undertake 3-D reconstructions, it is important to include alignment marks in the specimen so that individual slices or wafers can be vertically aligned on top of one another. This is best done by drilling vertical holes through the resin surrounding the specimen, or by cutting alignment groves in the exterior surfaces of the resin block. Once present these features are used as landmarks between successive surfaces and images centred in respect to these fixed points.
For further information, or to use the facilities, contact either Dr Jason Hilton or Dr Ivan Sansom