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Chris Campbell

Troubles With Curves

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Norm Stuart    80

Water treatment plants use Darvan at a lower concentration than we use in a ceramic studio - but they could use them at our higher concentration just as well, but it would cost more.  They use so much merely because they're dealing with such huge volumes of water.

 

Darvan is a polymer with long rows of charged areas which attach to clay particles.  Each long strand of plastic binds to a huge number of clay particles.

 

In a casting slip, Darvan gathers the clay particles together on each long strand, releasing a lot of excess water.

 

In a water treatment tank, Darvan gathers the clay particles together on each long strand, creating clay flocs, releasing a lot of excess water.  So a casting slip is a floc of clay.

 

When added to a glaze, Darvan binds to a wide range of particles quickly dispersing dry glaze materials - which is why glaze makers often use Darvan as a Dispersant in combination with flocculants like Calcium Chloride or tiny charged clay particles like Bentonite to suspend the dispersed glazed particles.

 

Sounds like Darvan is having an identity crisis! We have always used it as a deflocculant in slips. However if you add too much deflocculant to a slip, it will thicken up all nasty, like when chocolate siezes up. So maybe in higher concentrations it does the clumping in the water treatment plant.

 

Yes, technically a flocculated glaze would put less glaze per dip, but functionally I have not found it to be an issue. It's not thickening the glaze to the degree that a significant amount of water has to be added to get it to the proper fluidity for dipping. We use the same 6 count dip whether a glaze is deflocculated or not.

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Norm Stuart    80

Pat Horsley's "Score No More" formula uses both Bentonite and Darvan to add desirable properties to slip even though, in some circumstances shown above, one is a flocculant and the other a deflocculant.

 

The added Gum Arabic suspends the particles of slip but also creates a non-clay attachment mechanism between layers of clay as it dries.  Held in close proximity in the kiln, the feldspar in "Score No More" chemically bonds these clay layers together into one sintered object.

 

Ok Norm ... So translate floc/defloc to an easy to remember formula when working with slip ... so you can apply it to surfaces without it cracking as it dries .... I can never remember which I am supposed to do! Neither choice seems intuitive to me.

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Babs    386

Sounds right Babs ... So, a slip with less clay and more water needs to be flocculated?? ... Or de-flocculated?

It needs to be deflocculated.

Non scientific me, I'd evaporate, dry out the slip "manually, then get it back to a more fluid state by adding deflocc. drop by drop till it's the fluidity you want..Should be more clay particles in the state of fluidity you want . Still there?

Now I think.....DEflocc. DEhydrate (less water in the fluid)

I know you scientists!!!!,  just relax :rolleyes:

Living on  a sheep property I DO NOT want to think sheep, flocks of,  when I pot!

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Babs    386

 

Water treatment plants use Darvan at a lower concentration than we use in a ceramic studio - but they could use them at our higher concentration just as well, but it would cost more.  They use so much merely because they're dealing with such huge volumes of water.

 

Darvan is a polymer with long rows of charged areas which attach to clay particles.  Each long strand of plastic binds to a huge number of clay particles.

 

In a casting slip, Darvan gathers the clay particles together on each long strand, releasing a lot of excess water.

 

In a water treatment tank, Darvan gathers the clay particles together on each long strand, creating clay flocs, releasing a lot of excess water.  So a casting slip is a floc of clay.

 

When added to a glaze, Darvan binds to a wide range of particles quickly dispersing dry glaze materials - which is why glaze makers often use Darvan as a Dispersant in combination with flocculants like Calcium Chloride or tiny charged clay particles like Bentonite to suspend the dispersed glazed particles.

 

Sounds like Darvan is having an identity crisis! We have always used it as a deflocculant in slips. However if you add too much deflocculant to a slip, it will thicken up all nasty, like when chocolate siezes up. So maybe in higher concentrations it does the clumping in the water treatment plant.

 

Yes, technically a flocculated glaze would put less glaze per dip, but functionally I have not found it to be an issue. It's not thickening the glaze to the degree that a significant amount of water has to be added to get it to the proper fluidity for dipping. We use the same 6 count dip whether a glaze is deflocculated or not.

 

Two types of deflocc. the alkaline and the things like sod sil which deflooculate by a different action of the ions. So it is poss , depending on the quantity added to go OTT and get the flocc effect, I think. And this type of defloocc actually destroys the thixotropic qualities of clay.

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Norm Stuart    80

The polymer Darvan deflocculates glaze and slip by flocculating clay onto its plastic strands.

 

Flocculation (in polymer science):  Reversible formation of aggregates in which the particles are not in physical contact.  In contrast to aggregation, agglomeration is a reversible process.  This is why a water treatment plant sends the clay and Darvan to a landfill - even though the clay and the Darvan are not in physical contact, the static attraction is not reversible so the Darvan cannot be reused.

 

Flocculation (except in polymer science):  Process of contact and adhesion whereby dispersed molecules or particles are held together by weak physical interactions ultimately leading to phase separation by the formation of precipitates of larger than colloidal size.

 

It would not be correct if someone said "Darvan deflocculates clay" because actually "Darvan flocculates clay".  But Darvan does deflocculate glaze and slip which contain clay.

 

It's just like nebulous concept of "Clay Plasticity" where I need to distinguish between the "Cohesive Plasticity" of clay and the "Deformation Plasticity" of clay or any other type of plasticity clay exhibits.   http://community.ceramicartsdaily.org/topic/5492-the-mysteries-of-clay-plasticity/

 

I'm glad I followed this through, as it clarifies some aspects for me.

 

Sounds right Babs ... So, a slip with less clay and more water needs to be flocculated?? ... Or de-flocculated?

It needs to be deflocculated.

Non scientific me, I'd evaporate, dry out the slip "manually, then get it back to a more fluid state by adding deflocc. drop by drop till it's the fluidity you want..Should be more clay particles in the state of fluidity you want . Still there?

Now I think.....DEflocc. DEhydrate (less water in the fluid)

I know you scientists!!!!,  just relax :rolleyes:

Living on  a sheep property I DO NOT want to think sheep, flocks of,  when I pot!

 

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Babs    386

Don't know about Darvan,

The concept of defloc and floc are not nebulous in and of itself, manmade stuff, well certainly nebulous.

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Babs    386

Sounds right Babs ... So, a slip with less clay and more water needs to be flocculated?? ... Or de-flocculated?

The other thingie, going non scientific this am, is that ther e is a temptation to add water when you first look at your premade slip. Don't ever do this just stir, may look like cream cheese but with a bit of agitation, maybe that's what's wrong with me today, it will move into a more yoghurt-like state!! :)

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Norm Stuart    80

Thixotropy is the name for that non-scientific thing where something thick gets thin under pressure or movement.  We get a lot of that with a mix of water with either clay or gums.

Xanthan Gum regels instantly after rapid agitation, while clay slip and takes quite some time to regel.

 

 

Darvan aka Dispex is Sodium Polyacrylate a syrupy liquid which is added to detergent to sequester Magnesium and Calcium ions from hard water so the detergent cleans better, used as the agent for time-release medications bound to the polymer, and the reason you can drink clean water in cities.   In a related crystalline form it's the water absorbing gel in baby diapers, not to mention fake snow for Hollywood.  Shown here hydrating.

Much more versatile stuff than a sodium carbonate or sodium silicate rendering magnesium and calcium ions insoluble.  Quite useful stuff actually.  http://digitalfire.com/4sight/material/sodium_polyacrylate_1273.html

 

You'll find it in almost as many places as liquid PVA polyvinyl acrylate invented in 1912 or hydrolized as crystalline polyvinyl alcohol (Elmer's Glue, Wood Glue, Latex house paints, acrylic artist paints, gesso, sizing, paper coating, and carbon dioxide barrier in plastic soda bottles.  Just mix either with your studio whiting (calcium carbonate) and pigments like titanium, manganese, iron oxide and you've made your own latex house paint.

 

Make PVA from ethylene and you have ethylene vinyl acetate making yoga mats, wine corks, flip-flops, a higher quality latex house paint, running shoes, fishing floats, you're soaking in it now.  New clay technologies are opening a multitude of new artistic doors and avenues for you and you hadn't even noticed.


The other thingie, going non scientific this am, is that there is a temptation to add water when you first look at your premade slip. Don't ever do this just stir, may look like cream cheese but with a bit of agitation, maybe that's what's wrong with me today, it will move into a more yoghurt-like state!!

 

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Babs    386

Short shelf life even shorter bucket life, at its best a filler.

NOW back to Chris's problem with slip cracking and falling off pot.

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Chris Campbell    1,088

The discussion illustrates extremely well why I still have no clue and have to read up every time ... And problem two is my Darvan is at least ten years old! Of course, old Darvan could be my whole problem.

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Norm Stuart    80

I pretty confident you'd no longer have a problem of slip falling off if you mixed the Score No More ingredients in with your slips.

 

There's a lot to be said for adding a non-clay adhesive like the Gum Arabic or a few drops of Elmers Glue.  I use Xanthan Gum in our Score No More since we had no Gum Arabic.  Most manufacturers have long ago replaced Gum Arabic with pectin or engineered starches like EmulTru.  But with almost any type of gum if you don't get perfect clay to clay adhesion, the slip is still glued onto the clay and sinters together with the feldspar flux when it's fired.  The PVA glue is overkill for most situations, but I've used it in a number of cases - it's one of the key ingredients in my home-made bisque fix for those having ware with a tragic life.

 

There's certainly plenty of occasional unavoidable reasons why a slip might not stick to a clay - drying too fast, different stacking properties between the slip and the clay which is helped by adding bentonite to the slip, etc.  It doesn't have to be a problem of moisture or flocculation, although misting the clay with calcium chloride before apply the slip doesn't hurt. 

 

We just add Pat Horsley's magic ingredients so we don't have a problem with slip sticking to clay.  Remember that's why I ended up mixing our Mason Stains with Gerstley Borate - to eliminate bonding problems people experienced with some of the commercial under-glaze.  That problem stopped and has never happened again.

 

You can easily test your Darvan by mixing some with some glaze and see if the glaze has settled the next morning - if it does it's still good.  It's freezing liquid Darvan that really degrades it, and I keep it in a shed to avoid the UV.  We buy a pint of Darvan 811 once every two or three year or so.   I use it mostly as a dispersant and as one of the Score No More ingredients, and occasionally for the settling tank to avoid dumping sodium in our garden area.

 

Are there any particular clay or slip combinations which don't bond well?  Darvan 7 doesn't work well with heavy iron clays, which is why we buy the 811.

 

The discussion illustrates extremely well why I still have no clue and have to read up every time ... And problem two is my Darvan is at least ten years old! Of course, old Darvan could be my whole problem.

Edited by Norm Stuart

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Norm Stuart    80

You'll notice when John Britt adds the Darvan, he doesn't give the slip any time in the real-time video to settle which would enable him to pour off excess water - so the slip merely gets thin.

 

So instead John merely adds Epsom Salts to undo the effects of the Darvan, apart from its dispersant qualities, and adds additional clay to take up the excess water.

 

If you don't want to take the day or so to let the slip settle out, so you can pour off the excess water, you need to not add so much water with the Darvan in the first place.

 

In the second video when John Britt adds Darvan to a glaze which is too flocculated the effect on the viscosity is almost immediate, but the glaze still applies too thin on the bisque because, again, he hasn't given Darvan the time it needs to settle the glaze so he can pour off the excess water.  The only alternative to pouring off excess settled water the next day, would be to add more dry glaze - which was his quick solution to the slip as well.

 

Darvan works the same way in a water treatment plant.  After mixing the Darvan with the water, the mix slowly flows from tank to tank to another where it finally reaches the sand beds to be filtered out many hours later. You have to give it time to settle so you can eliminate the excess water.

Let's see what John Britt would say . . .



 

 

The discussion illustrates extremely well why I still have no clue and have to read up every time ... And problem two is my Darvan is at least ten years old! Of course, old Darvan could be my whole problem.

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ChenowethArts    461

There are more than a couple of threads going on here, and I have a question that relates to both.  I like the idea of mixing Pat Horsley's "Score No More" to slips...it sounds like a great solution to resolve Chris' slip-falling-off issue (there's joke there I'm sure, but I'm not going there).  But, since the Pat Horsley formula includes Darvan and Darvan, from what I have learned here, has a short(er) shelf life, does the Score No More have the same shelf life as the Darvan or is the shelf life shortened, extended, or not-affected by the Darvan component?

 

I'm still pretty old school when it comes to joinery. I do my best to make sure pieces are very similar in moisture content and use slip from the same clay on the scored surfaces to be joined...and then I compress the bejabbers out of it as it gets leather hard.  That bejabbering process probably knock the flock or de-flock out of my join issues ^_^

 

My son still swears by Lana Wilson's Magic Water formula for joining:

  • 1 gallon water
  • 3 tablespoons or 9.5 grams liquid sodium silicate
  • 1 1/2 teaspoons or 5 grams soda ash

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Pres    896

Lana Wilson's Magic Water formula for joining:

  • 1 gallon water
  • 3 tablespoons or 9.5 grams liquid sodium silicate
  • 1 1/2 teaspoons or 5 grams soda ash

I use it, I like it a lot.  I mix up a gallon and keep it in the shop always. I use a stiff toothbrush or cone shaped brush to apply it and work the joining area well. Since using it with HS students I had much fewer joins come apart and fewer seam cracks. So I decided it was a good thing.

 

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Norm Stuart    80

Score-No-More shelf-life is primarily determined by the gum you use.

 

If you use a gum with a biocide which protects the gum, it will also protect the Darvan from biological attack.

 

There are more than a couple of threads going on here, and I have a question that relates to both.  I like the idea of mixing Pat Horsley's "Score No More" to slips...it sounds like a great solution to resolve Chris' slip-falling-off issue (there's joke there I'm sure, but I'm not going there).  But, since the Pat Horsley formula includes Darvan and Darvan, from what I have learned here, has a short(er) shelf life, does the Score No More have the same shelf life as the Darvan or is the shelf life shortened, extended, or not-affected by the Darvan component?

 

I'm still pretty old school when it comes to joinery. I do my best to make sure pieces are very similar in moisture content and use slip from the same clay on the scored surfaces to be joined...and then I compress the bejabbers out of it as it gets leather hard.  That bejabbering process probably knock the flock or de-flock out of my join issues ^_^

 

My son still swears by Lana Wilson's Magic Water formula for joining:

  • 1 gallon water
  • 3 tablespoons or 9.5 grams liquid sodium silicate
  • 1 1/2 teaspoons or 5 grams soda ash

 

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Norm Stuart    80

Magic Water is both a deflocculant and a flux.  So it's the Darvan and Feldspar components of Score-No-More.

 

Score-No-More also has bentonite to fix stacking problems between two types of clay, and gum to provide non-clay adhesion between layers of clay which aren't bonded for any reason.

 

so is Magic Water a defloculant?

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Babs    386

Thanks Bcisket for the John Britt video and thanks Babs for hanging in here with me! ...

I understand now ... I learn best by seeing.

No worries mate! clarifies it to explain it, and yes, J britt did it in a nutshell, well a bucket or 2.

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Norm Stuart    80

The thing to remember using a deflocculant of any type is you need to give the slip enough time to settle out so you can pour off the excess water.  If you don't, the deflocculant is not actually reducing the water percentage of your slip.

 

Thanks Bcisket for the John Britt video and thanks Babs for hanging in here with me! ...
I understand now ... I learn best by seeing.

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Babs    386

 

The thing to remember using a deflocculant of any type is you need to give the slip enough time to settle out so you can pour off the excess water.  If you don't, the deflocculant is not actually reducing the water percentage of your slip.

 

Thanks Bcisket for the John Britt video and thanks Babs for hanging in here with me! ...

I understand now ... I learn best by seeing.

 

That is why J Britt got his initial slip bleedin' thick to start off!

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Chilly    330

Let's see what John Britt would say . . .

 

 

 

 

 

I've now watched these two videos several times, and I'm starting to understand.  Too much more info than that and I'll get all confused again.

 

What I need to do now is to purchase Darvan (I'm sure there is an alternative that is more readliy available in the UK - Sodium Dispex?) to thicken up my slip so I can have another go at slip trailing, and epsom salts to fix my glazes that pan at the bottom of the bucket.  Put the learning into practice and then I'll truly understand.  Reading and seeing only work so far, for me to really learn, I have to do it. 

 

Thanks for all the contributions, but some of the above has gone straight over the top of my head.  K.I.S.S.

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Norm Stuart    80

The generic name is Sodium Polyacrylate CAS number 9003-04-7 for Darvan 811, and Sodium Polymethacrylate CAS number 54193-36-1 for Darvan 7.

 

The CAS (Chemical Abstract Service) numbers are an international reference and can be used to call for any local brand name.  Other brand names are Dispex and Dolapix.

 

Bear in mind that to reduce the water content of slip or glaze, merely adding a deflocculant like Darvan like John Britt does is not sufficient.  You also need to let the clay particles settle, say over night, in order to pour off the excess water.  John Britt is constrained by the run time of the video, but he should have explained this.

 

 

Let's see what John Britt would say . . .



 

I've now watched these two videos several times, and I'm starting to understand.  Too much more info than that and I'll get all confused again.

 

What I need to do now is to purchase Darvan (I'm sure there is an alternative that is more readliy available in the UK - Sodium Dispex?) to thicken up my slip so I can have another go at slip trailing, and epsom salts to fix my glazes that pan at the bottom of the bucket.  Put the learning into practice and then I'll truly understand.  Reading and seeing only work so far, for me to really learn, I have to do it. 

 

Thanks for all the contributions, but some of the above has gone straight over the top of my head.  K.I.S.S.

 

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