Jump to content

Flocculation and deflocculation -- how much is enough?


Recommended Posts

Is there a way to accurately measure a glaze's degree of floc or defloc?  Or some sort of formula for adjusting it?  I stick my finger in and see how much it covers, then dump in some flocculent like epson salts and dip again.  I can see the difference -- but I'm never sure where to stop.

If there is no way to specifically measure it -- what are your favorite ways of estimating?

Link to post
Share on other sites

What do you wish to accomplish by adjusting "...degree of floc..." - exactly?

Maybe. Don't know. Yes, per prior (emphasis added):

***

My guess is you'll find slight adjustment of thixotropy may sometimes be necessary after some time sitting in the bucket.

I'm noting each glaze's sg in my glaze notebook. After adjusting sg to a) same as last time, else b) a bit more or less, due to prior results, I'll test thixotropy by stirring clockwise (easier on my wrist, thumb, elbow, shoulder...) to match the meter of Bob Marley's "Rastaman Vibrations"; on cessation of stirring, the mass continues to revolve for just under three rotations, then comes to a stop all together, and "bounces back" a bit when it does stop. From there, tweak as necessary. Compare/contrast glaze slurry (of about same sg) that needs thixotropic adjustment - the mass continues to revolve, and obvious currents of differing speeds shear against each other; there is no mass stop, nor bounce back. Of course, you are free to choose how to match up stir rate as you wish, as well as what direction, eh? Rock on.

See Tony Hansen's video

https://www.youtube.com/watch?v=Ck_69eGJons

***

I'm seeing easily discernable progression as I add small doses of Epsom salt (or vinegar):

  a) the mass revolves more together (less obvious currents of differing speeds that shear against each other)

  b) the mass revolves fewer times

  c) the mass stops more together (same time)

  d) the mass gels/stops and stretches a bit - the stretch reaches limit, then bounces back (really! watch the vid again) 

After treatment, the glaze still moves (behaves as a liquid); indeed, it sheets off the ware when poured out (lining) or lifted out (outside - I'm still glazing the inside and outside as separate operations). However, there's much (MUCH) less curtaining/dripping, for the glaze stops moving, more or less all together, boom. I don't see adjusting thixotropy as related to the thickness of the glaze film, no.

At Mr. Hansen points out, he's lowering the sg so the glaze will behave as a liquid when moving.

When next I have a glaze session, will report back on the test I'd described on your stoney matt glaze thread; it'll be a week or so yet...

 

Edited by Hulk
might need to lower the SG
Link to post
Share on other sites
1 minute ago, liambesaw said:

No, I hate bentonite with a passion :)

Interesting.  I am having trouble getting a glaze to flocculate and wondered why I shouldn't just put some bentonite in to make sure there is enough clay.  But I hesitated thinking there may be good reasons not to if there are "down sides" to bentonite.  I would love to know the reason for your displeasure with it.

Link to post
Share on other sites

i guess liam and i see different sides of the question.   i put bentonite into everything.   maybe his recipes are different than mine.  i have no chemistry knowledge, just bumbling along using recipes i have found work with my clay and work.   the origin of the recipe is important, min  gave me one that is super, i get some from books, from workshops and from asking other potters.  

Link to post
Share on other sites
18 minutes ago, Rick Wise said:

Interesting.  I am having trouble getting a glaze to flocculate and wondered why I shouldn't just put some bentonite in to make sure there is enough clay.  But I hesitated thinking there may be good reasons not to if there are "down sides" to bentonite.  I would love to know the reason for your displeasure with it.

It's difficult to mix in after the fact and usually makes glazes too juicy for me for lack of a better word.  I don't use glazes that lack clay, so maybe that's why I don't find it necessary.  I prefer veegumT or this stuff @Mark C.turned me onto called magma.  Bentonite can be pretty dirty too, but at 2% probably can't notice the iron.

I don't single fire so I don't need my glazes to be juicy.  I know single fire people use it for better glaze adhesion.

Link to post
Share on other sites

Back to the original question of how to measure flocculation/deflocculation, or viscosity. Always measure specific gravity first to ensure the correct ratio of water to solids for that particular glaze the way you use it (i.e., spray, dip, brush, which can be further affected by the cone you bisque to). Then get a Zahn cup (expensive) or a Ford cup (cheap knockoff) to measure viscosity. Painters need to adjust the viscosity of the paint they are spraying and use a Zahn cup. It is a small cup with a handle that extends above the rim of the cup and a hole of a specific size in the bottom. Dip the cup into the glaze to fill it to the rim, lift it out and time how long it takes for the cup to empty through the small hole. I set my dipping glazes to a specific gravity of around 1.45 and drain from a #4 Ford cup in about 6.5 seconds. That's the scientific method. Others may use the finger dip or count the swirls until it comes to rest after a vigorous stir. Whatever works for you.

Edited by Dick White
typos
Link to post
Share on other sites
6 hours ago, Rick Wise said:

I am having trouble getting a glaze to flocculate and wondered why I shouldn't just put some bentonite in to make sure there is enough clay.  

What’s the recipe, how long ago did you mix it up, did it work okay when freshly mixed? 

edit: I like Magma too but it does make the glaze take longer to dry. That stuff can float rocks.

Edited by Min
Link to post
Share on other sites
3 hours ago, Dick White said:

Back to the original question of how to measure flocculation/deflocculation, or viscosity. Always measure specific gravity first to ensure the correct ratio of water to solids for that particular glaze the way you use it (i.e., spray, dip, brush, which can be further affected by the cone you bisque to). Then get a Zahn cup (expensive) or a Ford cup (cheap knockoff) to measure viscosity. Painters need to adjust the viscosity of the paint they are spraying and use a Zahn cup. It is a small cup with a handle that extends above the rim of the cup and a hole of a specific size in the bottom. Dip the cup into the glaze to fill it to the rim, lift it out and time how long it takes for the cup to empty through the small hole. I set my dipping glazes to a specific gravity of around 1.45 and drain from a #4 Ford cup in about 6.5 seconds. That's the scientific method. Others may use the finger dip or count the swirls until it comes to rest after a vigorous stir. Whatever works for you.

So what is the relationship - if any - between viscosity and the extent of a glaze’ flocculation?  More viscosity more flocculation?

Link to post
Share on other sites
6 minutes ago, Rick Wise said:

So what is the relationship - if any - between viscosity and the extent of a glaze’ flocculation?  More viscosity more flocculation?

Partially, or as much as can be expected.  There are other factors like thixotropy, rheopecty, etc.  Like you can mix and put slip into a ford cup but it can also just sit in there and not drain at all. 

But the general idea is the more flocculated, the more viscous.

Link to post
Share on other sites
4 hours ago, liambesaw said:

Partially, or as much as can be expected.  There are other factors like thixotropy, rheopecty, etc.  Like you can mix and put slip into a ford cup but it can also just sit in there and not drain at all. 

But the general idea is the more flocculated, the more viscous.

And, not to put too fine a point on it, if you tried, you probably could flocculate a glaze slurry with so much epsom salt or calcium chloride (or overdeflocculate it with so much sodium silicate) that it too would just sit in the Ford cup and not drain. (That's another thing about the Zahn/Ford cups, they come with different bottom hole sizes, so the drain rate may be different. For example, one commercial glaze purveyor states in their instructions that it should empty from their Zahn cup in 18 seconds. Either that is one hella thick glaze (probably not), or their cup has one hella small hole (more likely).) The trick is to get the right balance of specific gravity and flocculation or deflocculation in your dipping glaze so that it applies the right thickness of glaze to your ware and then flows off nicely with no drips as you withdraw the piece from the bucket.

Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...

Important Information

By using this site, you agree to our Terms of Use.