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How to read hydrometer

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#1 cfsarver



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Posted 25 November 2013 - 06:21 PM

I have a glaze recipe that specifys a viscosity of '45 to 48' to use. My hydrometer is in increments of 2.000 up to top number of 1.000. Is the recipe asking for a viscosity of 1.45 to 1.48? Perhaps I need to go back to the source and check if it's printed correctly. I don't assume things these days.
Thanks to all you smart people out there.

#2 JBaymore



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Posted 26 November 2013 - 12:09 PM

I have my students make "relative" viscometers.  This tends to be more accurate for most ceramic glazes than the specific gravity done with a commercial or home-made hydormeter. 


While you can't "compare numbers" with others with this unit.... for you own glaze work from btach to batch it is pretty darn accurate.


Take a small metal or plastic can/container...... about the size of a Campbell's soup can.  Drill a 1/4 inch to 3/8 inch hole in the center of the bottom.  (Start with 1/4" ... and if you find objectionally long timing for how you like you glazes.... increase hole size slightly.)


Use a felt tip marker to draw a "fill to line" on the inside of the can.


Take a glaze that is already exactly the consistency you want for application...... and fill the can to the line with your finger over the hole.  Pop your finger off the hole and time how long it takes to empty (most digital watches have a stopwatch function these days).  Record this # with your glaze recipe.


When you mix new batches of that glaze,..... carefully adjust the water content until the drain time matches.





John Baymore
Adjunct Professor of Ceramics; New Hampshire Insitute of Art

Former Guest Professor, Wuxi Institute of Arts and Science, Yixing, China

Former President and Past President; Potters Council



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