Reply To: Revised HSG 248 “The Analysts’ Guide” 2021

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mmJean Prentice

    The final version of HSG 248 is now available and unfortunately not all technical errors have been corrected.

    Two critical bits of Appendix 2 have not been altered, namely
    A 2.13 requires “matched-pair binocular eyepieces of 8x or higher, one focusing (preferably non-rotatable). An eyepiece cross-hair graticule defining the vibration directions of the polariser and the analyser may also be used”  Ouch – there is nothing wrong with using a single ocular microscope and cross hairs are an essential!!!!  A2.32 mentions adjusting the cross hairs!

    A2.32 states “The back focal plane should be fully and evenly illuminated and the substage iris in focus. For Köhler or Köhler-type illumination the lamp filament should be in focus and completely fill the field of view (correct by adjusting the lamp housing)”  Second sentence – the lamp filament is NEVER visible with Kohler-type illumination

    The above 2 items are not the wording agreed by WG2 when this document was finalised well over 12 years ago.

    And in Appendix 4, information on aragonite (originally they called it Calcium Carbonate which is akin to calling all chrysotile Serpentine) has been dropped altogether instead of being corrected – and there are still misleading comments about the relief of some of the organic fibres.  Aragonite will crop up during monitoring of contaminated land sites and has been found in Rail Track hard core.

    Sorry – just hope that UKAS doesn’t try and implement all of A2.13 and A2.32!!!!

    Jean Prentice