Needles

 (with thanks to Stephen S.Nagy, M.D. and The Amateur Diatomist Vol.III. no. III.) 

Diatom needles are best made from plain glass capillary tubes and around 1.00mm is a good diameter. Tubes pretreated with heparin are best avoided for this usage as are LIP pre-calibrated pipettes in the UK. The pulling of the needles is two stage and best done with a small spirit lamp with an adjustable wick.

The first stage, with a flame of 5mm of wick, melts the tube to make a solid glass cylinder which is then pulled to a diameter which fits inside the barrel of the Luer needle holder. The tube is positioned above the flame and about 25mm of capillary is melted by passing it gently to and fro along the flame. The melted section is pulled until the requisite diameter is achieved.

The second stage uses a much cooler flame which is achieved by lowering the wick until 1mm is left exposed and the flame is only just large enough to remain burning. The tube is lowered slowly into the flame with a continuous tension on both ends until the glass melts. The continuous pull creates a smooth taper to a precise and sharp point - hopefully!

This last stage is a real 'dark art' and many things may go wrong. If the flame is not hot enough there will be a sudden and audible 'pop' leaving a truncated end rather than a fine point. Too hot and the point will draw out to be too long and thin (wispy) to be usable.

The point may turn out curved but will still be usable if the curved is not too pronounced.

The needle is easily mounted in the holder by sliding the needle shaft into the Luer holder and sealing with sucrose. This is done by picking up a crystal or two of sugar with a wet fine brush and wiping the crystals onto the glass needle where it enters the holder. The application of a drop of water or saliva will cause the sugar to dissolve and to be sucked into the Luer shaft by capillary action. The solution will dry and harden and the assembly is usable almost immediately.

Remove broken needle stumps by soaking in warm water.

Needles can be stored on a slide with a piece of double-sided adhesive placed across one end. The needles are held parallel to one another on the tape and the slide can be kept in a plastic slide holder for safe keeping.

Alternatively, a piece of foam can be glued into a box and the needle bases 'jabbed' into the foam which I think is a better method as there is less breakage in removing the needles.