LASAA LASAA

 

The observation of the calcified structures of the aquatic animals often request a several steps preparation: embedding in resin, sawing of thin slices of the embedded calcified structure, grinding then polishing before observation.

1 - Embedding

Several types of resin are available according to the use: epoxy resin which means great fluidity and small shrinkage, polyester resin which has a low price and a fast curing. Several silicon elastomer moulds are used or made according to the requested embedding shape. LASAA has a vacuum drying oven which allows faster resins curings thanks to temperature increase, and a low moisture rate. It also permits to degas some resins.

2 - Sawing

LASAA has several saws available in order to get thin slices in the blocks of resin :

 

• a wire saw allowing very thin slices (50 to 60 microns),

 

• a circular saw STRUERS ACCUTOM 50 allowing cuttings arranged in series,

• three low speed saws ISOMET allowing 100 microns thin slices with a good surface appearance.

  

 

3 - Pasting

To polish both faces of a thin slice of an embedded structure, you need to paste, and then remove your slice from the slide. To do so, the laboratory is equipped with two hotplates with thermostatic control. The paste is a thermostatic resin (Cristal Bond 405) which melts at 120°C.

4 - Grinding

A perfect flatness of the preparations is requested when observing with a Microscopic Electronic Beam or a Micro-Probe. This is reached through the use of a grinding machine, the same used by geologists. Our machine is a LM300 from ESCIL's. Eight slices can be ground at the same time, the differences between the thickness of the slices is at worst 5 microns. The abrasive powder is a 9 microns silicon carbide powder (which corresponds to 1000 in ASTM norms and FEPA)

Grinding can be hand made as well or with a polishing machine (ESC 200 from ESCIL's) with abrasive papers (Grains 400, 800 or 1200 in FEPA P norms corresponding approximatively to 35, 25 and 16 microns respectively or in ASTM norms to 320, 400 or 600 respectively).

5 - Polishing

The polishing can be made with different methods. It can be hand made, or with the polishing machine ESC 200 from ESCIL's, or with the polishing machine PLANOPOL-V from STRUERS'. The abrasives used are either polycristalline diamond suspensions (ranging from 3 to 0.3 microns) when the preparation is an epoxy one, or burnt alumin powders when the otolith is embedded in polyester resin.

6 - Observation

Observations can be made with a microscope or with a binocular. Our laboratory is equipped with 3 Olympus microscopes, 2 of them have a dry X100 magnification objective, a Leica microscope and 4 Leitz binoculars M3, M5, M8 and MZ8. The Leica microscope is also equipped with a dry X100 magnification objective, it has a phototube, a motorized stage which can be driven from a computer. Images can be digitized with a Kodak digital camera, or photographed colour or black and white with the Wild MPS48/52 modular photomicrographic system. Images can of course be directed towards monitors and printed out.

LEICA DMRE

LEICA MZ8

 

7 - Preservation of the preparations

The preparations are kept in wooden boxes, and if they are to be observed with a microprobe or a MEB, they are placed in a dry keeper.