Terrascope is a manufacturer of high quality sediment thin sections for archaeologists, geologists and soil scientists. Thin Section Making is a Craft and an Art. This page details how your samples will be treated with us. Specific methodologies can be applied to specific samples on request.
Guidance for shipping your samples to France
Terrascope will provide you with all the informations regarding customs requirements if you ship your samples to us from outside of Europe. We will also provide advices on packing your samples to prevent breakage and damage. We will acknowledge the reception of the parcel by email and register all the samples in the lab calendar as soon as we get them. Find are contact details here.
The samples are stored in the lab prior to their processing. Before impregnation, the sediment blocks have to dry as water would interfere with the polymerisation of the resin. Samples are opened and placed in polypropylene containers to dry at room temperature for 2-4 weeks. All the informations on the sample (sample code, orientation of the block, etc) are reported on the container.
When the sample is dry, a mix of polyester resin, styrene monomere and a hardener is pored on the sample progressively. The exact recipe of the resin mix can vary according to the nature of the sediment. The resin rises progressively by capillarity towards the top of the sample. When the top of the block is wet with resin, the sample is fully immerged in resin then placed in a vacuum chamber. The use of a vacuum chamber and the application of a light vacuum improve the penetration of the resin to the heart of the sediment block by sucking the air out without disturbing the sediment microstructure. After 4h in the vacuum chamber, the block is left at room temperature for 24h then placed in a temperature controlled ventilated cabinet for at least a week.
Locating the thin section within the block
When the resinated sample is fully cured, the block is cut with a water-cooled saw into slices of 0,5-1cm thick (see our video on Instagram 🎥). A special attention is dedicated to place the thin section where the researcher wants it and specific instructions are followed when given. The slice of indurated sediment is trimmed to the dimensions of the final thin section (4 different formats available) then left to dry (check our Instagram for pictures of slabs).
Thin section mounting
The sample slice is mounted on a 2mm glass by spreading resin mixed with a hardener on the sample and glue it to the glass, then place the slide under a press overnight. Next morning the sample is cleaned from the excess of resin that spreed under the press. The slide is placed in the grinding machine which can process 3-6 slides at a time, depending on the format.
Functioning of the grinding machine
The grinding machine is a Brot geology equipment designed to make pedological thin sections. The samples are hold vertically on a wheel towards which a vertical grinding wheel is advancing slowly (see our video on Instagram 🎥). The operator can monitor the advancing speed of the grinding wheel, from 5µm to 25µm per rotation of the samples. The grinding wheel is lubricated and cooled by mineral oil that also keeps the samples clean from grinding residues.
The objective of first grinding is to obtain a perfectly flat and smooth surface prior to final grinding. The slide is slowly ground until there is around 1mm of sample left on the glass. Then the surface of the sample is polished at minimum speed to produce a perfect surface.
This new surface is then mounted on a new glass. To make sure the glass is also perfectly flat, it is polished the same way in the machine. The resin mix used to glue the sample on the glass is placed in the vacuum chamber to extract as much air bubbles as possible before mounting. The resin is spread on the sample which is glued on the glass and placed under the press overnight.
Second grinding is the most crucial/dangerous step of the process as it will determine the quality of the thin section. In theory you have a perfectly flat sample mounted on a perfectly flat glass, so it should be straight forward to polish the sample until there is only 30µm of sample left on the glass and obtain a perfectly homogeneous thin section. But that almost never happens as we are talking of microns, so every detail/error has an impact on the final thin section: some dust trapped between the glass and the sample, an irregular pressure during mounting under the press, etc. During this step, the operator has to remain very vigilant and watch the grinding process all the time in case something goes wrong, to stop the machine and save the sample before the damages are beyond repair. If the sample is not grinding evenly, if it starts making a hole, grind from the bottom or whatever, the grinding is stopped. This step requires experience from the operator as sediments can look very different depending on their nature. Sand is almost transparent while peat remains very dark and thick. From the experience of the operator, his decisions and abilities to detect when the grinding is not going well depends the quality of the final thin section.
Third mounting and grinding
As explained above, thin section making rarely stops at second grinding. The not perfect slide is remounted on a new glass following the same process as for second mounting. As the thickness of the sample decreases, the possibility of mounting errors decreases. The slide is ground the same way and the operator has again to observe the whole process and stop the grinding when the required thickness is reached. The slide is checked under the microscope and if it is still too thick, put back to grinding.
After grinding, the slide is thoroughly wiped to remove all the oil. The sample code is inscribed on the glass as well as the orientation of the sample. Some researchers want their slides to be covered with a coverglass. It protects the thin section and improves the optical properties under the microscope (see our video on Instagram 🎥). However it also prevents to undertake geochemical analysis on the thin section so it depends on the research methodology that will be implemented.