The following instructions explain how to produce thin sections slides. The information will guide students, cleared by the geology department to work with the equipment in the sedimentology lab, in producing thin sections.

The production of thin sections makes it possible for persons, with skills in optical mineralogy, to identify minerals through their properties. These slides provide precise information on the mineralogy of samples, proportions of minerals in samples, texture, cleavage, birefringence, and the determination of refractive indices.

This manual is divided into the following sections:

I. Cutting samples down to size.

II. Preparing sample surfaces by grinding specimens to produce flat rock chips.

III. Adhering samples to glass slides.

IV. Trimming and reducing samples to thin section specifications.

V. Grinding specimen surfaces

VI. Cover slipping.

The instructions for each step must be followed precisely, in a sequential manner, for results to be optimal. Cited figures can be found at the back of the manual. Text in italics gives explanations for the techniques that you are doing. Text in bold is generally cautionary in nature.

Equipment Materials

Diamond slab saw 120 grit Carborundum

Diamond trim saw 240 grit Carborundum

Sink 400 grit Carborundum

Thin section machine 600 grit alumina

Lap wheels 9.5 micron grit alumina

(2) 1' x 2'glass sheets UV activated epoxy

Hot plate Thermal epoxy

Light source with UV bulbs Time set epoxy

Vacuum chamber Epoxy containers

Thin section template Plastic stir sticks 

Pencil with rubber eraser Petrographic slides

Part I - Hard samples

DANGER: Hood of saw must be closed. Safety goggles and lab coat must be put on before switching machine to on position. Flying chips and spray could damage eyesight.

1. Place sample to be cut down in the vice of one of the slab saws. (Fig. 1 & 2) Leave as much overhang as possible ( 3 cm) extending past the left side of the vice. 

2. The saw blade must be able to freely turn. Lock the sample holder down to the screw drive by sliding the locking handle on the lower right forward. NOTE: Test by pushing and pulling the sample. It should not move.

3. Shut the hood of the saw and press the on switch. NOTE: Stay with saw until cutting is complete. The sample can be heard falling.

4. When cutting is complete, press the off switch and wait for the saw blade to stop revolving. Open the hood and remove the excess rock from the vice grips and place aside. Take the sample to be used out of the saw and return the hood to closed position. 

NOTE: If sample disintegrated rather than being cut, Proceed to Part II on preparing soft, friable, or porous samples.

5. Clean sample with running warm water and soap to remove kerosine used in lubricating and cooling of saw.

CAUTION: Safety goggles, lab coat, and hearing protection must be worn before operation of trim saw. Flying chips could damage eyesight.

6. Place sample on hot plate at 95 degrees until dry.

7. Use thin section template to mark off an area approximately 1.5cm x 3cm with a permanent marker. (Fig. 3)

8. Using the trim saw, trim sample according to template. (Fig 4) 

CAUTION: Use care when cutting. Excessive torque will break the blade.

Part II - Impregnating Soft, friable, or porous samples

1. Place sample on hot plate an 95 degrees for two hours. (Fig. 5) (This will allow any water to evaporate from sample.)

2. When sample has been heated for the appropriate amount of time, remove from hot plate and allow to cool in plastic container.

3. Mix epoxy and hardener together as well as possible. NOTE: See instructions on epoxy to determine mixing proportion. 

CAUTION: Safety goggles must be worn. Risk of implosion exists.

4. Remove the lid of the vacuum chamber (Fig. 6) by twisting and pulling because vacuum grease forms a tight seal. NOTE: Use care so vacuum chamber is not dislodged from mount.

5. Place sample in container and add epoxy, mixing thoroughly. NOTE: Epoxy should be filled to the top of the container.

CAUTION: Confirm that exhaust air hole from vacuum chamber is venting into a fumehole, because hazardous fumes will be discharged from vacuum chamber. 

6. Place sample into the vacuum chamber and return the lid, making sure it is well seated. Turn switch, labelled main, on and observe that an indicator light has illuminated.

7. Turn pump to on position.

CAUTION: Watch gauge on the vacuum chamber and be sure that needle does not pass 90 kilopascals or 27 inches of mercury. Implosion can result. 

8. When gauge begins to approach 90 kilpascals or 27 inches of mercury, turn pump off. NOTE: The vacuum will remain, but decrease with time.

9. Observe sample to see air bubbles being released. After 30 to 45 seconds begin to release vacuum with release valve.

CAUTION: When releasing pressure, be sure to do so slowly. Failure to do this can result in epoxy being splattered in the chamber. 

10. Return pressure in vacuum chamber to atmospheric pressure, and return release valve to closed position.

11. Repeat steps 8 through 11 until no air bubbles emerge from sample when in vacuum. 

12. Remove sample from vacuum chamber and allow to cure for 24 hours. NOTE: Do not heat. Heating will cause expansion of remaining air bubbles.

13. Clean any spilled epoxy from vacuum chamber and return to normal resting position.

14. Return to Part I, Step I for firm specimens.

Part I - Lap wheel

1. Turn on water to sink containing lap wheel.

CAUTION: Do not place hands under lap wheel when running due to risk of injury. 

2. Turn lap wheel to on position and wet the rotating wheel. Use a scrubber to clean wheel. (Fig.7)

3. Sprinkle the 240 grit Carborundum on the wheel, and while holding the sample chip firmly, with one of the two wide faces facing down, begin rotating the sample on the wheel surface in the opposite direction from which the wheel is turning. (Fig. 8). Cover the whole lap wheel with each pass so as to minimize damage to the wheel. NOTE: Rotating should continue for two to four minutes while periodically sprinkling 240 grit Carborundum and water on the wheel to maintain a paste consistency.

4. Wash both sample as well as wheel thoroughly. NOTE: Move faucet away from lap wheel so that waste drops do not fall on wheel.

NOTE: Failure to wash sample thoroughly can result in contamination of grit size on wheel, causing inadequate grinding or specimen damage.

5. Repeat steps 2 through 4 with the 400 grit Carborundum, and use the same side of the sample that was used for the 240 grit Carborundum. 

6. When finished rinse lap wheel with water and allow to spin dry.

7. Turn lap wheel to off position. 

Part II - Glass sheets

1. Uncover the two glass sheets and set cover aside.

2. Add 600 grit Carborundum and water to the glass sheet designated for 600 grit Carborundum. This should produce a slurry.

3. Rub the sample over the glass sheets in a figure eight pattern for 1 to 3 minutes. (Fig. 9) Be sure to cover the entire glass sheet so that it is evenly worn. NOTE: The same side of the sample should be used on the glass sheets as was used in Part I.

NOTE: If sample does not move smoothly, or if scratching can be heard, the glass sheet has been contaminated and must be thoroughly washed. 

4. Wash sample thoroughly.

5. Repeat steps 1 through 4 using 9.5 micron powder and the glass sheet designated for 9.5 micron powder.

6. Dry sample. If sample was not impregnated using the vacuum chamber then place on hot plate at 200 degrees until dry with the prepared side facing up. If sample was impregnated 

by vacuum chamber then it must dry overnight.

7. Replace lid over the glass sheets to avoid contamination.

1. Wash a slide in a grease cutting soap. NOTE: After slide has been washed, take care to only handle the slide by the edges. Failure to handle properly can affect the epoxy.

2. Dry slide by placing on a hot plate at 100 degrees, until dry, with the frosted side of the slide facing up or let the slide air dry for 2 hours.

3. Remove the sample as well as the slide from the hot plate and allow to cool to room temperature.

Part I - Mounting the sample chip using UV Epoxy

NOTE: The following steps will make use of the UV activated Loctite epoxy, petrographic slides, and a pencil.

1. Add three to four drops of Loctight epoxy to the prepared surface of the sample chip. (Fig. 10)

2. Next take the petrographic slide and place it on the sample chip with the frosted side of the slide facing the prepared surface of the sample chip.

3. Use the eraser side of the pencil to move the slide back and forth so that the epoxy forms a very thin layer between the chip and the slide. Continue to use the eraser to move all air bubbles from between the slide and the chip by pushing down with the eraser and moving the slide around to walk the bubbles to the edge. NOTE: This process should be continued until there are no more bubbles left in the slide.

4. Position the slide on the chip so that one end of the slide has a margin greater than the other end. There should be enough room to allow the slide to be labelled.

5. Carefully flip the slide over so that it does not become dislodged, and place it on the UV light assembly. Turn the light on and allow to sit for five minutes. The sample should be fully set at this point.

IMPORTANT: Once epoxy is set, use a carbide tip engraver to engrave the sample number on the back of the slide.

Part II - Mounting the sample chip with time activated epoxy

NOTE: Time activate epoxy is used on rocks possessing a preferred weakness. This will make use of the epoxy, a catalyst, a petrographic slide, and a pencil.

1. Mix together the epoxy and catalyst in a plastic weighing bowl. The ratio for the mixture of the epoxy is 100 parts epoxy to 34 parts catalyst. NOTE: The epoxy and the catalyst must be thoroughly mixed to form a homogeneous mixture.

2. Add three to four drops of epoxy to the prepared surface of the sample chip. 

3. Take a petrographic slide and place it on the sample chip with the frosted side of the slide facing the prepared surface of the sample chip.

4. Use the eraser side of the pencil to move the slide back and forth so that the epoxy forms a very thin layer between the chip and the slide. Continue to use the eraser to move all air bubbles from between the slide and the chip by pushing down with the eraser and moving the slide around to walk the bubbles to the edge. NOTE: This process should be continued until there are no more bubbles left in the slide.

5. Position the slide on the chip so that one end of the slide has a margin greater than the other end. There should be enough room to allow the slide to be labelled.

6. Carefully flip the slide over so that it does not become dislodged, and place aside for 24 hours.

NOTE: Once epoxy is set, use a carbide tip engraver to engrave the sample number on the back of the slide.

Part I - Thin section machine. (Fig. 11)

CAUTION: Lab coat, eye protection, and ear protection must be worn for Section IV.

1. Turn on pumps and motor to the thin section machine. 

2. Using the black knob, turn on the water to the cutting blade.

3. Place the sample into the holding arm of the cutting blade. The glass should rest against the two stops. (Fig. 12)

CAUTION: When using the thin section machine, do not apply to much pressure to the blade. This can result in putting to much torque on the blade and may cause it or the sample to break.

4. Begin to feed the sample slowly into the blade. Apply only enough pressure so that the sample cuts gradually. The sample will tend to feed itself.

5. When cutting is complete, remove the sample from the arm and go to the next step.

6. Wash sample thoroughly to remove any grit that was caused by cutting.

Part II - Grinding the sample

1. Using the black knob, turn on the water to the grinding lap.

2. Place sample in holding arm of the grinding lap.(Fig. 13) NOTE: The arm will be on the opposite side of the machine for the cutting blade. 

3. Turn the screw arm located in the front of the machine away from you to ensure the arm is going to have enough clearance. The gauge on the micrometer should therefore turn counter clockwise.

4. Begin to move the arm in a back and forth motion while turning the dial of the micrometer towards you. Continue to turn the dial until a grinding noise is heard. Make four to five 

complete passes across the grinding blade to ensure to the sample is evenly ground.

5. Turn the dial of the micrometer towards you two to three notches and repeat the grinding by making four to five passes over the grinding wheel.

6. Repeat step 5 until the sample is about 40 microns in thickness. At this point the thin section should be held to a light to see if any differences in thickness exist. 

NOTE: The following step cannot be rushed or damage to the slide will result causing it to be useless.

7. Return the sample to the grinding blade and continue to cut until the sample is between 32 and 35 microns. 

8. Take the sample and place it under the microscope under polarized light. (Fig. 14) If the sample is at the appropriate thickness, the quartz and feldspars will appear to be blue to 

red. If these colors are not observed then the sample must be returned to the grinding lap.

Part I - Glass Sheets

1. Uncover the two glass sheets and set cover aside.

2. Add 600 grit Carborundum and water to the glass sheet designated for 600 grit Carborundum. This should produce a slurry.

3. Hold the sample with two fingers or a thumb placed directly in the middle of the sample. Rub the sample over the glass sheets in a figure eight pattern for 5 to 10 seconds. Be sure to cover the entire glass sheet so that it is evenly worn. 

NOTE: Apply only enough pressure to be able to move the slide in the figure eight pattern. Too much pressure can cause minerals (especially quartz) to shatter or too much material can be removed. If sample does not move smoothly, or if scratching can be heard, the glass sheet has been contaminated and must be thoroughly washed.

4. Wash sample thoroughly.

5. Take the slide to the petrographic microscope to confirm thickness. If the birefringence is coming down quickly then extreme caution should be taken. NOTE: The quartz should be observed to be a uniform yellow when the thin section has reached desired thickness. If the quartz is not yellow then repeat steps 1 through 5 with care. If yellow is achieved then proceed to step 6.

6. Repeat steps 1 through 4 using 9.5 micron powder and the glass sheet designated for 9.5 micron powder.

7. Confirm thickness with the petrography microscope. If the slide has reached standard thickness, the quartz will appear to be grey with a yellow hue, and the feldspars will be a uniform grey. NOTE: If the desired color is not achieved then repeat steps 5 and 6.

8. Wash sample thoroughly and set aside to dry overnight.

9. Replace lid over the glass sheets to avoid contamination.

NOTE: The following steps will make use of the UV activated Loctite epoxy, cover slips, and a pencil.
 
 

1. Add three to four drops of Loctight epoxy to the prepared surface of the sample 

2. Use a lint free cloth to clean the cover slip to ensure that no grease is present.

3. Take the cover slip and place it on the sample 

4. Use the eraser side of the pencil to move the slide back and forth so that the epoxy forms a very thin layer between the sample and the slide. (Fig.15) Continue to use the eraser to move all air bubbles from between the slide and the chip by pushing down with the eraser and moving the slide around to walk the bubbles to the edge. NOTE: This process should be continued until there are no more bubbles left in the slide.

5. Position the cover slip on the sample so that it is covering as much of the sample as possible.

6. Place sample on the UV light assembly. Turn the light on and allow to sit for five minutes. The sample should be fully set at this point. NOTE: Clean bottom of slide before placing on the UV light so that it does not adhere to the glass.