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Pottery Knowledge Quiz Of The Week (Pkqw): Week 3

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Pres    896

In response to those that desire more on the materials end of things. . . 

 

Week 3

 

  1. Today, glass is made of silica, the glass forming oxide, plus oxides that cause the refractory silica to melt at a lower temperature. What other component is needed here to create a glaze, to hold the molten glass on a vertical surface?

  1. any metallic oxide

  2. silica

  3. clay

  4. alumina

  1. A starting point for many glazes could be a 50/50 blend of materials. Often a test is made on a clay tile to test the melting of the material. Beginners are often encouraged to create these tests to begin to understand what goes on with materials, and how to measure mix materials. These 50/50 tests are called _____________ __________.

    1. melt pads

    2. fusion buttons

    3. test tiles

    4. sample melts

 

  1. ___________ Is the process of pre-melting materials together, either in a laboratory crucible in your own kiln, or commercially in large batches. Doing so, renders poisonous oxides, non-poisonous oxides and soluble oxides insoluble.

      1. Fusion

      2. Crucible firing

      3. Fritting

      4. Water smoking

 

  1. Edward Orton developed the Orton cone system at Ohio State University, whereas Hermann Seger originally developed Seger cones at the Royal Porcelain Factory in Berlin. Most potters when using this method will set 3 cones in clay to be fired with the bisque, or glaze firing. These clay cone sets are called__________ ________.

      1. cone packs

      2. kiln setters

      3. draw trials

      4. optical pyrometers

 

 

 

This weeks questions were taken from text in The Craft and Art of Clay, Fourth Edition, Susan Peterson, Jan Peterson, Overlook Press, Woodstock & New York, c. 2003

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glazenerd    816

 

1. alumina

2. test tiles

3. fritting       (not fretting)

4. cone packs

It should be noted that I merely copied and pasted LT's answers because I agreed. This should be distinguished from looking over his shoulder and cheating :o  

 

Nerd

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LeeU    328

Alumina, fusion buttons (flow test), fritting , & cone packs.

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Denice    243

4,3,3,1  Question number two is a little tricky it could be a Fusion Button but is requires a crucible and more technical experience.  I think test tile is a straight forward answer for a student.    Denice

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Pres    896

If you have the book, by all means, get it out and look up the answers.   This is an open book quiz!

 

Oh, and on another note. Those of you that do not have the book, I can highly recommend it. It is very well documented with glaze tests, fusion button tests, color blending techniques, firing materials, and a most excellent compendium. This compendium includes pertinent information on oxides, chemical compositions, how to calculate glaze to formula and to batch, melting points, listing and analysis of frits used in the US, and a section of Artists techniques. It is a great book for any Ceramic library.

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Pres    896

Interesting to see the variety of answers and some of the justifications. Thing of it is if you run the right term, you come up with lots of articles on line; run a poor term, and you get . . . . 

 

For those of you interested in ceramic basics of clay and glaze you may find this article of use.

 

http://claybucket.com/wp-content/uploads/cadaily-RawMaterials_2.pdf

 

best, 

Pres

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Pres    896

I will be away most of tomorrow, but will post the full answers to the Quiz of the Week, Week 3 tomorrow afternoon/evening. However, you may the correct answers are in S. Dean's & LeeU's postings.

 

 

 

 

 

best,

Pres

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Pres    896

Answers:

 

  1. 4) alumina-Today, glass is made of silica, the glass-forming oxide plus oxides that cause the refractory silica to melt a lower temperature. The fluxes used in glass are soda and lead. Glaze contains at least one more component than glass to hold the molten glass on the vertical surface: alumina. Alumina is the chemical binder in glaze, and it also controls viscosity; its usual source in glaze is clay itself. Some of you may argue that I was unfair in that I included clay in the listing. However, if you look at the question, the hint to the answer was in the raw component mentioned-Silica.

  2. 2) fusion buttons-Fusion buttons are made by tamping a given material — mixed almost dry with just a drop of Water — into a thimble, crucible, or other small cupped volume and inverting it onto a tile. If you make your own tests, use a flat tile made of a White clay body with sides high enough to contain a melt if one occurs. The bottom of each tile should be labeled with the name of the material and the temperature of firing.

  3. 3) Fritting-Fritting is the process of pre-melting materials together, either in a laboratory crucible in your own kiln, or commercially in big batches. This renders poisonous oxides non-poisonous and soluble oxides insoluble. The molten mass is crystallized (sintered) when poured into cold water and reground into fine powder.

  4. 1) cone packs-Making cone packs. To allow cone packs to dry, make them in advance of firing. Use clay mixed with grog, sawdust, etc., for the cone-bed, and poke holes in the wet clay to allow moisture to escape. Use only enough clay to hold the cones, not a great wad. Disaster occurs when cone packs blow up in the kiln because they are not dry enough; this means that the final temperature cannot be read, and the cone shards will stick to the glazed pieces.. . . . . . A number of cone packs can be used to record the temperature in various parts of the kiln, or to assess the evenness of ï¬ring; but a pack of three cones is always placed in front of each viewing hole, or at least on decks at the bottom and top of the firing space.

 

I hope that everyone had refreshed their memory of some things, or learned something new.

 

best,

Pres

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JBaymore    1,432

Answers:

 

  1. ".......This renders poisonous oxides non-poisonous and soluble oxides insoluble."

 

I think that this statement is an overly broad generalization and not necessarily true in all cases.

 

best,

 

....................john

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John,

 

Ok,
I can accept that Peterson's assertion is a generalization.

 

Perhaps you can start a new thread and discuss the why it is "overly broad," and specifically discuss the oxides that fall into the "not necessarily true in all cases" category.

What are those oxides and why are those frits not insoluble?  Data would help.

 

 

 

 

Answers:

 

  1. ".......This renders poisonous oxides non-poisonous and soluble oxides insoluble."

 

I think that this statement is an overly broad generalization and not necessarily true in all cases.

 

best,

 

....................john

 

 

 

LT

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JBaymore    1,432

John,

 

Ok,

I can accept that Peterson's assertion is a generalization.

 

Perhaps you can start a new thread and discuss the why it is "overly broad," and specifically discuss the oxides that fall into the "not necessarily true in all cases" category.

What are those oxides and why are those frits not insoluble?  Data would help.

 

 

 

 

Answers:

 

  1. ".......This renders poisonous oxides non-poisonous and soluble oxides insoluble."

 

I think that this statement is an overly broad generalization and not necessarily true in all cases.

 

best,

 

....................john

 

 

 

LT

 

It is actually a pretty simple concept and it is not about specific oxides.  It is about understanding what a stable glaze/glass melt is.  WHOLE other can-o-worms.

 

We all (I believe) already acknowledge that some glazes are unstable and can leach certain materials in bases or acids.  This is a pretty well documented piece of information.  If you "buy" that concept to start with..... then remember........ all a frit is, is an already melted glaze/glass that has been fused and made back into a powder.  If the formulation of that glaze/glass (that we'll then call a frit after processing) is not stable......... the frit is also not stable.

 

I can weigh out a pile of white lead and a pile of flint.  Stuff them in a crucible, melt them, pour into water, ball mill the 'visually looking like a glass' stuff into a powder....and have what I'll now call a frit.  If the molecular ratio is off... I don't get 'lead bisilicate'.  The ratio of lead oxide to silicon dioxide must be correct to get the reduced bio-availability of lead.

 

I can make a frit.... but it won't be stable.

 

The implication in that above broad answer statement is that you can just make a frit out of anything and then it is stable. Melt it first into a glass... and all is well.  That, as stated, could be misleading to some people with less technical savvy........ but who could/will go out and make a frit because the FIRING part of the process is relatively simple and doable with simple equipment.  And assume that simply by performing the FIRING end of the process... they have solved some issues.

 

best,

 

.......................john

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glazenerd    816

John:

The question was to you, so I was waiting for you to answer first.

 

The chemistry behind this question is thermal decomposition. OSHA has this guideline about thermal decomposition that states after a certain point of heat, then the offending bio-hazard has been rendered "cleansed." However, just because an element is melted, does not mean it has decomposed into separate "non-hazardous" molecules. You have to break apart (decompose) the chemical bond of the molecules to technically render a harmful substance-safe. Our glazes melt in general from 2000 to 2300F. They melt yes, but many do not break apart  (break their chemical bonds) until 3000-5000F.  Thought I would add the specifics to this question.

 

Nerd

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John, et .al.,

 

I fully agree that any glaze should be stable for use as the maker designed the object (including the glaze) to be used. 

 

I understand your point of view regarding the frits used in a glaze, and agree that the frit itself should also be 'stable' for use as the frit is intended to be used - as an intermediate ingredient between raw materials and a properly formulated glass (or glaze).   

 

My interpretation of Peterson's entire paragraph, from which Pres drew the quoted answer to his question, was exactly what you were emphasizing, even though she did not explicitly say that.  My background and experience just assumed that a frit maker (because, after all, he is a frit maker by trade) would know that just melting lead and silica together would not be sufficient to convert the lead to a 'stable' non-toxic and insoluble (in water) state .  You explanation shows that my (and probably Peterson's) assumption could be a false assumption.

 

You have provided an excellent example of why generalized statements in textbooks (and in forum discussions, and magazine articles) can be misleading in many ways unless carefully written to limit application to the appropriate context.  The same goes for simplified explanations of the many processes used in the production of ceramic objects.
 
 
Thank you for pointing out a consequence of generalization and for providing a complete answer to my question.
 
LT

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JBaymore    1,432

The main reason I brought it up the way I did was because I know people who make their own frits.  It is those "assumptions" that get us in trouble.  Yes... pro commercial frit makers know what they are doing (hopefully ;) ).  But you never know what people reading stuff will do with it.

 

best,

 

...................john

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Pres    896

I am very happy to see that there is some contentious discussion of this issue. I will not say that I had chosen that question and answer with a crystal ball, but I did see that there were problems saying melting anything together would make a frit. Interesting point/question is a definition of frit. So I returned to Internet searches on the definition of frit. . . . . . before ever posting the question. Here is the best thought I could find, and it comes from a source I usually think reliable. . . Ceramic Arts Daily:

 

Combinations of ceramic materials that have been melted to a glass and crushed/ground back to a powder, in order to give greater chemical stability and to eliminate toxicity resulting from water solubility of raw material. All frits are ground glass and are toxic in inhalation. FERRO 3124—high-alumina calcium-borate frit, gives greater strength in LT claybodies. FERRO 3134—calcium-borate frit often used as substitute for Gerstley borate in low-fire glazes when greater reliability and/or long-term insolubility and/or greater transparency are desired. Makes good cone 04 transparent glaze by itself. FERRO 3110 and 3195—Both very similar to 3134—run tests to determine which works best for your needs. Source: Clay: A Studio Handbook

 

 

Happily,

best,

Pres

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