Lou,
 
Best bet is to have your saponifier supplier come in and do some training for free. They can set you up with titration process, which is much more definitive than refractometry.
 
The issue with refractometry is that it measures the dissolved solids in the solution as a sum. While you can be confident of the saponifier concentration with clean water, as the contaminants are taken off the circuit board they collect in the wash water. This becomes part of what the refractometer reads and can force the measurement off a bit.
 
Titration uses an indicator and very precise wet measurements, so skill level is quite a bit higher than use of the refractometer, however, it is selective, therefore voiding the "dirty water syndrome". Titration, FYI, is the process you use to determing the chlorine and ph levels in your swimming pool.
 
If you are realy ambitious, you might want to correlate the titration measurements vs. refractometer over different times of day for a week or so to determine just how far off the refractometer truly is. You might be suprised at the results, i.e., if  your production volume is very low, it will be quite close, but if your production volume is high it can be way off, like to an order of magnitude!
 
Regards,
 
Ed Popielarski
QTA Machine
10 Mc Laren, Ste. D
Irvine, Ca. 92618
 
Ph: 949-581-6601
Fx: 949-581-2448
 
http://www.qta.net
 
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