Use of an arc: freezing and storing a crystal

• Establish a 'standard' pin length that will keep the crystal in the centre of the arc as it is rotated. Ensure that all your pins and top hats conform to the standard length
• Mount the crystal on the arc base and freeze it using a Cryostream
• Once the sample is frozen and ready to store, label a cryovial and cryocane
• Fill a 2 litre intermediate Dewar with liquid nitrogen
• Take a glass sample handling Dewar and also fill it with liquid nitrogen. Place the labelled vial in the vial holder (or the vial tweezers) and submerge them both in the liquid nitrogen, contained in the glass sample handling Dewar
• Rotate the goniometer so that the arc attachment screw hole is upwards. Attach the removable arc. If the Cryostream nozzle is in the way, rack it back to create more room for maneuvering
• Rotate the top hat on the arc so that it is pointing downwards by pushing the horizontal metal bar around gently
• Put on a pair of cryogloves. Bring the glass sample handling Dewar, containing the vial holder and vial, as close to the goniometer as possible. Inside the generator housing is ideal
• Remove the vial holder from the glass sample handling Dewar and place the vial full of liquid nitrogen in the vial holder
• Bring the vial holder and vial full of liquid nitrogen up under the pin and carefully enclose the top hat in the vial
• Move the vial holder SIDEWAYS to break the magnetic hold of the magnetic base on the top hat. If necessary use the forefinger of your free hand to nudge the top hat sideways from the other side of the holding magnet
• Try not to panic at this stage. You have approximately 25 seconds to complete this stage before the liquid nitrogen will boil off to below the position of your crystal in the vial
• As soon as the top hat and sample are inside the frozen vial, return the vial holder and vial to the glass sample handling Dewar so that the vial and sample are fully submerged in liquid nitrogen
• It is important to note that if a lid is to be placed on the vial, a blowhole should be drilled in the lid before it is used. It is recommended that the lid is placed on the vial if canes with lateral extrusions (to rest the vial base on) are to be used
• Next, bring the vial holder up so that the top of the vial just breaks the surface of the liquid nitrogen. Put the lid on the end of the lid opener and screw it on the vial. Do NOT screw the lid on too tightly as vial lids sometimes freeze on and can be very hard to get off
• Immerse the whole vial and lid in the liquid nitrogen until the surface of the liquid nitrogen goes flat and equilibrium is reached
• Lift the vial holder and vial from the glass sample handling Dewar and remove the vial. Put the vial holder down. With the free hand lift the pre-labelled cane out of the 2 litre Dewar and place the vial on it at the next free position, working from the bottom of the cane upwards
• Make a note of the crystal shape, the marking on the vial and cane and the date. When the canes are full, transfer them to the main storage Dewar all at the same time. This avoids opening and closing the storage Dewar unnecessarily, preventing ingress of moisture from the air

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