New Here, Have Question About Duncan Glaze Shivering?

[arcadiax]

Hello everyone,

 

I am new to the forum and I came here to seek help and guidance regarding shivering of my glazes. I am also quite new in ceramics in general, having just started working with ceramics as a hobby on my own around 1.5 year ago.

 

I have many of the old duncan lines of glazes, small jars of crystal tones, art tones, speckle tone etc, and they glazes that purchased in whole batches from a local ceramic supplies store auction from private individuals and they all seem to be shivering off of my clay. the glazes have not been tampered with and are factory default although some had dried up in their jars so I rejuvenated them with water.

 

Application wise, I spray my glazes on most of the time - 2-3 coats. brushing is usually 2 coats.

 

I mix my own batch of clay and only fire to low cone 04 - 05 for glazes and cone 02 - 03 for bisque. the new spectrum glazes seem to be slightly better although they also shiver if it is glossy.

 

The chemistry of my low fire clay is quite straight forward and I got the recipe off of digital fire. It is a low fire talc body clay consisting of 50/50 talc (American talc) and ball clay (KT brand) with a tiny fraction of a percentage of feldspar. I use something called a Minsbar that was purchased from my ceramics store and they said it is feldspar. I also have nephelium synenite which I have not tried yet.

 

The shivering symptoms are all on point, always near the edges and corners and on all pieces that have glossy glazes so I assume it has something to do with the glass component involved thus the thermo expansion / contraction rate between clay and glaze fit. It has gotten pretty bad that the shivering occasionally are sending explosive tiny shards flying - time bombs. None has gone so bad to have cracked any clay bodies yet however. 

 

Having done some research on my own thus far, I am still hesitant and would just like a final word from a master or someone with more experience before I start bulk adding some things into my glazes or to buy / mix a new low fire clay body all together for testing purposes. I just do not truly know what to add especially when it comes to frit types / boron.

 

My wares are for decorative purposes only so porosity or the shock test is not a huge issue for me as these will not be used for eating or drinking hence low fire in the first place. it is also to save money because high firing does cost more.

 

I have a couple of different types of frits on hand - with the majority being frit 3124-2 (Not sure what the dash 2 means). The other ones are frit 3466 (Leaded), frit 3396, frit 3489 (Leaded). I assume from reading the lead helps even further lower the frit's melting point.

 

Some people are saying boron is a super melter and helps conform glazes to bodies very well. 

 

My current glaze firing cycle is around 8-10 hours long with average being 9 hours. 

 

I am thinking maybe mixing a new batch of clay that better conforms to my duncan glazes might be more time saving and also resource saving but any suggestions are welcomed and I will try them all out!

 

Please ask any questions that you may need and I will answer them to the best of my abilities. 

 

Thanks for reading, I look forward to any replies.

 

- Steven

 

 

[glazenerd]

Hi Arca:

 

Will not address the premix glazes or the low firing schedule: I do not deal with either. Will let others who deal with them, address them.

 

I do however know some things about:

 

 

I mix my own batch of clay and only fire to low cone 04

and

 

The chemistry of my low fire clay is quite straight forward and I got the recipe off of digital fire. It is a low fire talc body clay consisting of 50/50 talc (American talc) and ball clay (KT brand) with a tiny fraction of a percentage of feldspar.

 

Talc is high in magnesium, and a fair amount of silica: but little else in the way of fluxes. KT ball clay virtually has no fluxes, and about the same amount of silica as talc. I do not know what a "fraction of feldspar" means in relation to percentages. This blend is on the very low side in regards to silica: it would produce a somewhat weak body. More importantly: not even remotely enough flux to vitrify in a low fire. Not to mention not the perfect flux for this firing schedule.

I ran very extensive test of flux percentages in clay bodies not that long ago: setting formula limits for cone 6 and 10. That aside, when flux percentages fall below a certain level in the clay: shivering occurs. I would expect to see a fair amount of clay debris on the back of the shivered glaze. I would also suspect that the shivering problem is rather extreme. The last piece of evidence it is the clay body: ALL of your glazes are shivering.

I do not deal with low fire clay bodies for the most part: but I do know the flux percentages usually run well above 40% of total batch weight. By just adding the flux percentages in talc and KT: you have less than 2% total. In low fire bodies, frits are used extensively because they melt at lower temperatures than feldspars. So I would be looking hard at your clay body, not the glazes.

 

Nerd

[curt]

Nerd, have you put the results of your clay body flux testing on the forums? Did a quick search but could not find anything like that.

[arcadiax]

Hi Nerd,

 

Thank you so much for your reply. 

 

The amount of feldspar (Written as soda ash in the digital fire recipe) was at 0.1% of total dry materials. They also mentioned adding some whiting to help with moisture expansion, which is something I am unfamiliar with and have not added in yet.

 

This is the link to the recipe page: https://digitalfire.com/4sight/education/low_fire_white_talc_casting_body_recipe_250.html

 

In regards to the fluxes proportion you had mentioned, yes I do not think I saw anywhere in the recipe where they mentioned to add flux hence I have not added any fluxes to the recipe.

 

I don't know why, but I've always thought of glass and clay to be separate realms and for clay bodies it usually has to be mostly clay - not glass. I know, weird of me but it's just one of those idiot ways of thinking. This is why I never dived to deeply into fluxes and clay bodies, mostly just fluxes and glazes (Because glazes - traditionally and mainstream-wise to me - are glasses mostly at least when I think about it). Lots for me to learn still.

 

You are also right, the shivering is taking quite a bit of clay debris along with it.

 

Nerd, I understand you mentioned that you do not deal with low fire clay, but could you maybe point me in a direction for me to perform some further tests? You mentioned low fire bodies having sometimes <40% flux in dry batch weight, do you know more info about this where I can read it up more, or someone you know who might be able to give me some pointers?

 

Pretty much all the symptoms I am experiencing are on point and your guesses are also on point. I just don't really know what to take next, even for further testing purposes.

 

For me, I am not really an experimental ceramicist, but just want to take a stable and straight route with 1-2 commonly used clays that fit well with most commercial glazes. 

 

Thanks again nerd!

 

- Steven

[glazenerd]

GM Steven:

 

First off:

 

I know, weird of me but it's just one of those idiot ways of thinking.

 

Self deprecation will not solve the problem: and it bothers me when people do that to themselves. Ignorance is the lack of knowledge which is easily fixed, and stupidity is the inability to learn. I commend you for walking out into the waters of uncertainty.

 

Although the text books describe the problem you are facing as shivering: that is actually incorrect. Shivering, like crazing is a COE (expansion) issue, You are dealing with scaling; due to the lack of bonding: which is due to the lack of vitrification. Clay becomes a glassy matrix just like your glaze does: just different parameters. ( simple definition) When the clay  does not vitrify, large pieces of it pull away and adhere to the glaze.

 

Joel (High Bridge Pottery) just posted a link to a low fire clay recipe in just the past week. I ran that formula: it has good limits, and produces a good working body. The recipe you posted from digitalfire is a casting body actually: Tony gives a warning about it in the article.

 

Firing and fired properties had to be compromised to get the easy working properties. Firing is done at cone 06, that is a very low temperature, there is no getting around it. Pieces are weak, you can rip them apart with your bare hands easily. They are completely unsuitable for functional uses.

Low fire clays almost always use frits because they melt in the 1450-1650F range. Many feldspars just begin to melt at the low fire temps you are trying to work in.

 

 

Curt: the only information I have posted about limits was in the "porcelain survey" thread- pg3 ( I think) I have sent some of my findings to Ron Roy, and we have been discussing back and forth additional parameters at this point. The problem Steven is describing begins when fluxes fall below 18% at c6, and intensify as they continue to fall. Which also means if they are visible at 18%, there are still problems at 20-22%: just not readily apparent. It will be awhile yet before I would be comfortable with releasing info. Once I get them narrowed down: would like to have them MOR tested for confirmation. For now; it is test-test-test. Where I have heard that before? 

 

Nerd

 

Link that Joel posted:

http://ceramicartsda...ch-to-fritware/

 

 

Mu cup is empty, so to the jobsite I go. Joseph: my last day at the flipper house. Finally, after 5 months.

[arcadiax]

Hi again nerd,

 

Fluxes are essentially just grounded up glass right? I've worked with decals and usually I was taught to apply a thin layer of flux so the decal adhere's better to the underlying fired glaze. Hence why I've always thought of fluxes as something that we should only add in small quantities and specifically glaze related. 

 

I've never thought of it as people adding over 40 or 50% to entire clay body mixtures. It's ignorance pure ignorance on my part and I totally understand your reply because ignorance in ceramics can be dangerous.

 

Nerd, I will try out Joel's recipe after having taken a look at it, but with the recipe from Digital fire, is there anyway to salvage it by adding something into the mix and testing it out? I just don't want it to go to waste and I have about roughly 4 gallons left of that slip mix. I can even let the slip dry on my plaster bats first so they reach dry weight before applying anything if that works better for your suggestions.

 

I forgot to mention, I actually do slip casting and make my own molds hence why I found that recipe.

 

Nerd, thanks so much!!!!!!!

 

- Steven

[arcadiax]

Oh Nerd, I just took a look at the recipe you sent from Joel and I have a question. For fritware, it says it is for cone 04-03. Can I bisque it to cone 02 or so? I understand with glass, it sags so I don't want a disaster...

 

- Steven H.

[arcadiax]

Oh Nerd sorry but I have just another question. 

 

Can I use the current talc I have - american talc brand? The recipe says pioneer or west tx talc?

 

- Steven

[glazenerd]

Hi Steven:

 

Just woke up from my old man nap. Went in at 6am this morning to finish up a flip house I started 5 months ago.

 

Very little difference in talcs, silica, alumina, and magnesium vary a bit from each. Some rare exceptions. White talc sold on the market is usually grey talc that has been calcined to remove the carbons. Really not a concern. The talc is more for thermal expansion issues, than anything.

 

As far as bisque to 02: not really my area: but I seem to recall reading those guidelines before. Hopefully, someone who fires in this range can add to the firing schedules.

 

After checking one thing: lets try these two very simple recipes using the talc and clay you already have.

 

1/3rd each of talc, KT and 3124 frit.          second recipe 1/3rd each of talc, KT, and gerstley borate.

Make 300 grams of each body= 100 grams of each add.  Simple math.

 

Make a 4 x 4 tile of each recipe: throw the rest out, or play with it if you want.  Fire each tile to maturity 04-05 (no glaze).   Weigh each tile after firing and enter weight. Then boil both in water for two hours, pat dry and enter weight. Weight difference equals absorption: will need to know that number. It will give a fair indication of vitrification. Be sure to identify each with markings: they will look the same after firing. Be sure to cut them exactly 4" x 4". Measure them after the boil test: will give some indication of shrinkage: although it does not conform to shrink test parameters. It will suffice for now.

 

Then you get to do the poor mans vitrification test ( safety glasses required). Smack each one dead center with a hammer, with enough force to break them, but do not overdo it. A vitrified clay will shatter in large angular pieces, and glass like shards will appear where you made the strike. An immature clay will break in an irregular pattern: and be more "dust" like where you made the strike. Cheap, not overly scientific, but gives some indication: besides its fun.

 

Run these two bodies first: then post the results. Will take it from there.

 

Nerd

[glazenerd]

Edit note on recipes:

 

The recipes shown will still be considered weak because the silica amount is only 59%, and the alumina % is just over 15. It will work, just not a very strong clay body. Silica should be well over 60, but 59% is acceptable (barely). The problem child is 15% alumina: it should be 22-27%.

 

Nerd

[arcadiax]

Hi Nerd,

 

You've been wonderful so far, thank you.

 

I will try out the homework you had provided. I don't have gertsley borate but I will go buy some. I bisque 1-2 cones higher for a cleaner burn so later during glazing, no dirtiness from the clay body will come through the glaze since I won't be hitting the same temperature again. It's just a little something I had picked up online from some people's suggestions.

 

I am ok with a clay body that is not the strongest since these things I make (Decorative figures) are purely for display purposes so they will not be functional wares.

 

OK so before I attempt your test, I just want to double check with you. 

 

My current recipe is pretty much at 50/50 ball clay-talc. I will just add another 50 frit 3124 / gertsley borate to the batch (Or isolated batch portion) and go from there right?

 

Also, your second post just above this one, you mentioned recipe(s) - are you talking about both joel's and digital fires or just 1 of them? What would happen if we were to try to increase the alumina to the desired amount (And could that increase be applied to both recipes or just one of them)?

 

Thanks Nerd!

 

- Steven

[glazenerd]

Recipe # 1

 

100 grams talc, 100 grams KT ball, and 100 grams frit 3124

 

Recipe # 2

 

100 grams talc, 100 grams KT ball clay, and 100 grams Gerstley Borate.

 

If you want to add 2% alumina hydrate to increase alumina ratios- feel free. Alumina is usually sourced from the clays and feldspars: but there are no set rules that say you cannot just add it.  Make sure you blend well.

 

Nerd:

[arcadiax]

Nerd, with alumina hydrate, what happens if we add too much or too little of it? Any adverse effects?

 

Thanks Nerd!

 

- Steven

[glazenerd]

Steven:

 

Way too much alumina, and you will have a kiln shelf instead of a clay body; and your glaze will do all kinds of fun stuff on it. Too little means too weak: and COE issues are magnified; showing up as split pieces, cracks.. etc. Porcelain and stoneware bodies run 22-29% alumina: earthenware and low fire clay typically run 20-24% alumina.

 

If you have ever been by or seen pictures of  hi-rise buildings being built: the steel skeleton (beams) carry all the weight of the building. All the glass, brick, stone, and plaster are just decorative coverings for visual effect. Alumina works the same way in glazes and clays: it is the interlocking girder system that gives both their strength. All the colorants, stains, and enhancers are just for visual effect. Silica is the primary glass former in glaze: too little of it: you have no glaze. In clay, silica content is also a requirement to build the glassy matrix.  Look at it this way: silica is the brick, and alumina is the mortar: got to have both.

 

Nerd

[PeterH]

Hi,

 

Sorry that you are having problems. Can you confirm that your starting recipe is:

Talc         50.0

Ball Clay  50.0

-----

Water                 45.0% of dry amount

Soda Ash           0.1% of dry amount

Sodium Silicate  0.2-0.4% of dry amount

 

... and say exactly what changes you have made to it (e.g. amount of water, feldspar, bentonite, ...).

 

How do you make your wares: hand-building, throwing or slip-casting?

 

Regards, Peter

 

 

 

 

[arcadiax]

Hi Nerd,

 

Alumina Hydrate, is that an alloy (Aluminium) or something completely different?

 

And thanks so much for the in-depth analogy, you drew an awesome picture that is very clear.

 

Silica, I think in its pure form requires quite a high temperature to melt hence people added lead or boron or other ingredients to help lower the melting point of it, is that right? 

 

Nerd, this might sound a little redundant, but Joel's recipe does not have any Alumina,. Is it because Alumina is already present in all the other ingredients or...?

 

Thanks Nerd.

[arcadiax]

Hi,

 

Sorry that you are having problems. Can you confirm that your starting recipe is:

Talc         50.0

Ball Clay  50.0

-----

Water                 45.0% of dry amount

Soda Ash           0.1% of dry amount

Sodium Silicate  0.2-0.4% of dry amount

 

... and say exactly what changes you have made to it (e.g. amount of water, feldspar, bentonite, ...).

 

How do you make your wares: hand-building, throwing or slip-casting?

 

Regards, Peter

 

Hi Peter,

 

Thanks for reading my thread. For that recipe I used a 5 gallon bucket but the actual material did not make 5 gallons - around 2.5 gallons. 

 

I did all my measurements in grams, even converting water weight to grams - wasn't sure if that was correct way but keeping the measuring units all the same made things simpler. 

 

For this one, I added the exact amounts as indicated in the recipes, except I think instead of adding sodium silicate, I added southern bentonite 0.4%. And for soda ash, I used feldspar (Minspar 200) and added 0.1% amount.

 

One strange thing though is I could never get the gravity right to start with that recipe as my slip would come out way too thick in the end so I end up adding more water to thin it  - I know it's wrong. The casting come out alright though in the end, except they do shrink more than I'd like inside the mold - hence sometimes causing some premature cracks in the more detailed molds.

 

What should I do in this case? I remember if you added too much deflocculant, it would thicken the slip up but I added the recommended amount from the recipe? Could the recipe be at fault?

 

And yes Peter, for my method, I do slip casting.

 

- Steven

[glazenerd]

Steven:

 

Joels' recipe cited above has 26.31% (molar) alumina and 56.36% silica.  Clay is primarily silica and alumina in different ratios. Secondly clay is rated in particle size ( grain size). Fire and stoneware clays tend to be larger, porcelain intermediate, and earthenware smaller: always exceptions to that general rule. The other general rule: the finer the particle size: the more plastic (flexible) the clay is. Ball clay is generally finer grained: hence ball clay/s are more plastic than kaolin.

 

An alloy is a blend of two or more metals. Alumina oxide (oxidation state). http://www.axner.com/alumina-hydrate.aspx

 

The typical melting range of silica without flux additions is 3150F. However, again particle size plays a role in that as well. I use Imsil A25 primarily because of its purity level, but also because its particle size only requires 2950F to melt. Flux additions are required to lower the melting temperature of silica, and most clays for that fact.

 

Joels recipe requires 1% macalod: which is fairly expensive product.  Replace the macaloid with 4% bentonite or L10 (white) bentonite. However, be sure to thoroughly blend in the bentonite before adding liquids to ensure even disbursement.

 

Nerd

[Min]

 

Hi,

 

Sorry that you are having problems. Can you confirm that your starting recipe is:

Talc         50.0

Ball Clay  50.0

-----

Water                 45.0% of dry amount

Soda Ash           0.1% of dry amount

Sodium Silicate  0.2-0.4% of dry amount

 

... and say exactly what changes you have made to it (e.g. amount of water, feldspar, bentonite, ...).

 

How do you make your wares: hand-building, throwing or slip-casting?

 

Regards, Peter

 

Hi Peter,

 

Thanks for reading my thread. For that recipe I used a 5 gallon bucket but the actual material did not make 5 gallons - around 2.5 gallons. 

 

I did all my measurements in grams, even converting water weight to grams - wasn't sure if that was correct way but keeping the measuring units all the same made things simpler. 

 

For this one, I added the exact amounts as indicated in the recipes, except I think instead of adding sodium silicate, I added southern bentonite 0.4%. And for soda ash, I used feldspar (Minspar 200) and added 0.1% amount.

 

One strange thing though is I could never get the gravity right to start with that recipe as my slip would come out way too thick in the end so I end up adding more water to thin it  - I know it's wrong. The casting come out alright though in the end, except they do shrink more than I'd like inside the mold - hence sometimes causing some premature cracks in the more detailed molds.

 

What should I do in this case? I remember if you added too much deflocculant, it would thicken the slip up but I added the recommended amount from the recipe? Could the recipe be at fault?

 

And yes Peter, for my method, I do slip casting.

 

- Steven

 

 

You really can’t sub a feldspar (the minspar you used if I read your post correctly) and bentonite for the deflocculants that were called for. The soda ash with sodium silicate work together to deflocculate the casting slip. 

 

Laguna article on adjusting casting slips here: http://www.lagunaclay.com/support/art-of-slipmaking.php

[PeterH]

You really can’t sub a feldspar (the minspar you used if I read your post correctly) and bentonite for the deflocculants that were called for. The soda ash with sodium silicate work together to deflocculate the casting slip.

 

As Min said.

 

(Also Digitalfire advises Do not put bentonite in the casting version of this body, the casting rate will slow down dramatically.)

 

The amazing differences in the property of slips with different level of flocculation can be seen in

a couple of John Britt videos:

 

 

... as these videos are not aimed at a slip-casting audience I would just take the message that

control of the state of [de]flocculation is important. Then  I would re-read the article Min mentioned.

 

Here is another article which discusses deflocculating a slip (using a different deflocculant) which

highlights the problems of deflocculating just enough but not too much.

 

Go with Digitalfire's recipe as a starting point, and get both the density and viscosity in the right ball-park.

 

Then try glaze-tests again, as there is no guarantee that this will have fixed you problem .

 

=============================================

 

If you still have shivering problems, there are [at least] two course of action you might try.

 

1) Tweaking Digitalfire's recipe, some possibilities are:

1a) Switching to a different ball-clay, or a mixture of ball-clays (I have no suggestions here).

1b) Invert Digitalfire's advice for crazing -- If crazing is a perennial problem, then use more talc

      and less ball clay -- by using more ball-clay and less talc.

 

2) Start another thread asking  for recipes for a cone 04 - 05 casting slip.

 

 

 

[glazenerd]

Peter / Min / Steven:

 

That is part of the problem in this thread: two different clay bodies are being discussed.

 

The original thread started with a slip cast body, and then added the topic of low fire frit ware body (Joels recipe).

 

Everyone needs to be clear which recipe they are addressing.

 

Nerd

 

Edit: need to slap my own hands in going back through my own posts. I am jumping back and forth between recipe % and weight %: bad Nerd!!

[arcadiax]

Hi Nerd

 

You've been fabulous. I truly am grateful to have you helping me out on this forum. Before, in the early stages of my self taught ceramics journey, most things have been hit and miss and I count myself as extremely lucky in not having encountered any major disasters with equipment.

 

In regards to Joels recipe, I won't change anything and will follow exactly as he had written it. I just went out and purchased all the necessary ingredients needed plus the macaloid as well. 

 

Nerd, you mentioned L10 bentonite (White). Is that similar to Southern Bentonite. I think I have something called Southern Bentonite - the one my store sold to me. Would this one suffice or should I get the White Bentonite?

 

Nerd, I had read over Joel's recipe and although he uses it for wheel throwing in his examples, can you help me out in the ratios of turning it into a slip for casting? I am just a little unsure whether all universal slip are 45% water ratio and the same amount of defllocculants (As is with my initial recipe from Digital Fire - 0.2% - 0.4%) or if the ratios are different depending on the type of composition / recipe mixed? 

 

I wanted to mention, I have both sodium silicate and Darvan as deflocculants. I read online that Darvan is much more forgiving than sodium silicate if you over add as it won't over thicken the slip.

 

Also, I do have an old school gravity tool - not sure if that is the correct term. It looks like one of those very steep, semi enclosed spoon with a small hole. You just scoop and the slip flows through the hole at the bottom. I was always told you've got good gravity / viscosity if your slip flows like thick cream continuously through the hole.

 

I know for sure we need water in the slip lol *Dry Sarcasm*...

 

Thanks Nerd!!!!

 

- Steven

 

------------------------------------------

 

Hi Min,

 

Thanks for checking out this newbies thread. I appreciate it.

 

Also, huge error on my part.

 

I meant to say I added the Darvan I had instead of Sodium Silicate. I was told Darvan is much more forgiving than Sodium Silicate in case I messed up going over slightly in measurement. Online, people said Sodium Silicate, easily over thickens.

 

I also added the Southern Bentonite for plasticity just in case I needed to work with the clay slightly by hand after slip casting.

 

For Minspar 200, I was told it is the same thing as Feldspar by my ceramic store? They sold that to me. Can you confirm Min?

 

- Steven

 

------------------------------------------

 

Hi Peter, 

 

Thank you so much for your resources in deflocculating. I am planning to try out Joel's recipe that Nerd in this thread had provided at the beginning. 

 

If it still does not work, I will start a new thread asking people about low fire clay body recipes that work well with commercial glazes. I will also search for such recipes in the forum as well.

 

I'll keep you and everyone posted.

 

- Steven

 

 

[glazenerd]

Hi Steven:

 

 

I just went out and purchased all the necessary ingredients needed plus the macaloid as well.

 

Macaloid is like salt and pepper: every potter adds it according to their taste. Joel's recipe: the potter added the macaloid to adjust it to the plasticity level of his own working preferences. Mix a 500 gram recipe: let it age 24-36 hours before you use it so it will hydrate completely. Use it in your technique and note how it works for you: the feel, the resiliency, the strength, firmness, etc. If you feel it is too pliable, then lower the macaloid additions. If it cracks readily, feels stiff in your hands: then raise the macaloid to 1.5% and blend again.

 

 

Nerd, you mentioned L10 bentonite (White). Is that similar to Southern Bentonite. I think I have something called Southern Bentonite - the one my store sold to me. Would this one suffice or should I get the White Bentonite?

Bentonite (bentones) are like talc: the same basic composition with variances in mineral composition. The pottery industry generally refers to them as clay: even though they are actually not. Macaloid is highly plastic, and L10 is plastic: so it takes more L10 to do the job that just a little macalod does. All bentonites are ultra fine particle size: making them the grease of the clay body that makes everything move around more freely: hence plasticity. (notice the lack of heady chemistry terms .....they make my head hurt!.

 

Slip casting is not my thing. Darvan is much more flexible and forgiving than sodium. I will let Min or Peter walk you through that part of the equation.

 

Nerd

[Min]

------------------------------------------

 

Hi Min,

 

Thanks for checking out this newbies thread. I appreciate it.

 

Also, huge error on my part.

 

I meant to say I added the Darvan I had instead of Sodium Silicate. I was told Darvan is much more forgiving than Sodium Silicate in case I messed up going over slightly in measurement. Online, people said Sodium Silicate, easily over thickens.

 

I also added the Southern Bentonite for plasticity just in case I needed to work with the clay slightly by hand after slip casting.

 

For Minspar 200, I was told it is the same thing as Feldspar by my ceramic store? They sold that to me. Can you confirm Min?

 

- Steven

 

------------------------------------------

 

Hi Steven,

 

Glad the oopsies was just in this post and not in the bucket! 

 

Yup, Minspar is a (soda) feldspar.

 

The spoon type device you have sounds like a version of a Ford cup, used for measuring viscosity,  you count in seconds the time it takes to drain.

 

How much water to add is part of the alchemy of all this. 45% sounds high to me but testing the specific gravity of the slip multiple times during mixing is the only way to find out how much to add. 

 

I don't know how plastic that fritware body Joel posted is but usually casting bodies are far less plastic than throwing bodies. Really don't know if it would work as a casting body, I'm guessing here but I think it would be better for casting if you left the bentonite out. Which is more critical a good casting body or one you can throw with?

 

Just in case you haven't come across it here is a super good page of info that covers a lot of info on slip casting, maybe grab a cup of tea before you read it, it's a long one: https://digitalfire.com/4sight/education/understanding_the_deflocculation_process_in_slip_casting_213.html

 

I think Peter's idea of starting another post and asking for low fire white slipware bodies is a good one.

 

edit: One other thing, in your post #17, you mentioned subbing something for the sodium silicate and the slip was too thick. So, if you used darvan instead of sodium silicate at the same amount this would explain why the slip was too thick. Darvan isn't as strong as sodium silicate therefore you need to use a bit more of it. Go by the specific gravity not by how thick it looks.