Deflocculating An Old Brushing Glaze

[mrcasey]

We have some old brushing glazes in pint containers.  The glazes haven't been used for

almost 5 years.  Some of the containers are almost full, but the glazes are as thick as

Greek yogurt.  The fact that the containers are so full tells me they haven't lost much water.

I dropped about a tablespoon of darvan 7 into one of the containers, mixed it up,

but it didn't thin out much.  I feel like that much darvan should have deflocculated the glaze.

 

Any thoughts?

 

 

  

 

 

       

[Magnolia Mud Research]

If the glazes contain Gerstley-borate, the gelling is normal and deflocculating is not needed.  Take a small mixer and stir the 'yogurt' and run a test piece.  

 

LT

 

defloc-ing the glaze will likely make it settle into a hard lump. 

[neilestrick]

I wouldn't deflocculate them. Take a little bit and add water and see how it brushes. If it doesn't brush well, like it dries really fast, then you'll need to add gum solution.

[Dick White]

Commercial glazes and underglazes often have an organic gum brushing agent which deteriorates and decomposes over time. The glaze can often be restored by adding new gum solution. As Neil points out, adding just water to thin it may not work.

[Benzine]

I have this issue with a few of my commercial classroom glazes.  Amaco's Old Pewter is the worst offender.  Myself and my students like the glaze, but it does like to thicken in the jar.  If I would try to use it, as it was, or with a bit of water to thin it the glaze would crack after application.  Darvan didn't do anything of note good or bad.

I never thought to try gum, but that will be my next step, if it happens again.  I have successfully used gum in some of my underglazes that thinned out.  They were usually the ones that smelled like a sewer full of rotting eggs.  My class had certain jars, that you could tell were being used from anywhere in the room.  I'd be helping students, *sniff*, *sniff*, "Alright, who is using the green underglaze?...."