Improved Reference Standards for Reflectance Measurement

Reflectance reference standards play a vital role in the quality assessment of coking coals for export and coke-making processes. The aim of this project was to improve the design of reflectance reference standards used in coal petrography, especially for new-generation imaging systems, and provide a wider range of reflectance values than was currently available commercially. The new standard was then tested by leading laboratories involved in coal analysis. 

The participating laboratories were: 

• ACIRL
• BHP Billiton Newcastle Technology Centre 
• Carl Zeiss Imaging Solutions GmbH
• Coal & Organic Petrology Pty Ltd
• CSIRO Queensland Centre for Advanced Technology  

The reflectance reference standards which are currently available are designed for spot measurement devices and they produce accurate readings when used with these devices. However, most of these standards are not ideal for calibrating imaging systems since they do not provide accurate reflectance readings at every point in an image. In this project a new design was developed experimentally using the MACE®300/OPTICOAL® System, an automated coal petrography system developed with ACARP assistance under Projects C6055, C8056 and C11022.  
The improved design used five different optical glass segments with reflectance values of 0.130 %, 0.304 %, 0.497%, 1.00 %, and 1.96 %. The segment dimensions were up to four times larger than traditional designs. This reduced parasitic light effects, for example, uneven lighting due to glare was reduced by up to 92 %. The reflectance reference standards and materials developed in this project will be made available to the Australian coal industry by Jenkins-Kwan Technology Pty Ltd.  To assist makers of in-house standards this report also provides technical and materials selection information for up to 50 different glasses with reflectance values in the range 0.1 % - 2.0 %.  The total cost of this project was $36,000 of which $23,600 was provided by ACARP. 

Finally, it is recommended that at the next review of Australian Standard™ AS 2856.3, it should be updated to include advice on the use of reflectance reference standards suitable for microscopy by imaging systems.