My studio gets very dry, and the glaze bucket does loose its water content in a span of two weeks even with the lid on. I draw a line on the interior wall of the bucket when finish glazing so I knew when it lost water.
When I glaze, I usually check the thickness of the glaze by using the hydrometer or weighting the glaze (10 cc). And I still had inconsistent results of the glazed ware. I suspected the Epsom salt being the cause. I use the Epsom salt as the flocculant, which slows the settling of the glaze.
Last time, I mixed the new batch of glaze; I did not add the Epsom salt and tested the new batch of glaze in the last firing. (Test, test test! I do measure carefully, but I still mess up time to time. ) Now I can mix with old batch of the glaze safely. I checked the thickness by weighing 250 cc of the glaze this time; first the glaze without the Epsom salt, then added the Epsom salt in the glaze. Both weights came up 275 g. The result showed the Epsom salt does not interfere with the weight of the glaze. I guess 10 cc was too small of sample. I did not test today, but I was very sure the hydrometer was inaccurate with the glaze containing the Epsom salt.