The Polishing Rush

Anna Funke

The last weeks of term are always a challenge in getting everything finished, but this term one task in particular – polishing SEM samples – took its toll on everybody’s patience.

The SEM (Scanning Electron Microscope) is a powerful analytical tool for our work. However, the sample preparation process is rather tedious. Just a quick reminder, a scanning electron microscope uses an electron beam (rather than light with standard optical microscopy) to produce images up to 500,000 x magnification.

Although there are several different methods for preparing these samples, our technique involved mounting our samples in resin (Clear Casting Resin POLYLITE 32032-00 from Alex Tiranti Ltd., to be specific), using ice-cube trays as moulds.

1

Resin-cast samples of glass beads prepared by Emily Williams.

2

An SEM image of the above sample, as prepared by Emily Williams. The glass appears grey in this image, and the swirls show that the glass was poorly mixed. The white specks in the sample are unmelted metal colorants in the glass.

Once cast, the resin block has to be prepared and sawn into the correct shape. This often requires some elbow grease and several sacrificial saw blades. The sample is then polished to the smoothest possible surface. This required four grades of abrasive paper, followed by 4 grades of micro mesh that added up to a good 5 hours per sample. One of the challenges is to make sure you are not left with scratches all over your sample.

The polishing work station of Megan Narvey.

The polishing work station of Megan Narvey.

The author and Megan Narvey discovering a significant amount of scratches on their samples.

The author and Megan Narvey discovering a significant amount of scratches on their samples.

At the end this long process you should have a shiny smooth resin surface, and are likely to have repetitive strain disorder. But if, against all odds, you do succeed in preparing a beautifully smooth surface, the images you will get in return for your labour are really quite amazing!

Sample of a cross-section of a painting by Kristen Gillette. Layers 1, 2, and 3 are surface pigments, probably acrylic paints; Layer 4 is a pigment ground layer; Layer 5 is the ground; and Layer 6 is animal skin.

Vanessa Applebaum’s cross section of painted plaster along with elemental maps of the sample.  Explain what can be seen here

Vanessa Applebaum’s cross section of painted plaster along with elemental maps of the sample. The cross section shows the plaster, applied pigment, and a carbonation layer. The elemental maps identify where specific elements are located in the sample. They are, starting from the top and moving left to right: silica, iron, chlorine, calcium, titanium, aluminium, potassium, and sodium.

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