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I developed this test primarily to test clays: you will not find it in text books- it is being introduced for the first time. 

Split LOI Test

 
Loss on ignition is a chemistry term, measuring the amount of organic/inorganic material released from solids, when they are heated to a temperature that is high enough to produce combustion. In pottery/ceramics, the definition is widened and application broader. LOI is applied to minerals such as silica, feldspars, talc, dolomite, and other commonly used glaze ingredients. In addition, LOI is also applied to clays, bentonites, plasticizers, and hectorites. 
 
LOI of clay is considered when trying to calculate the properties of raw clay or blended bodies. LOI for individual raw clay is an important value for judging the suitability for use in a blended body. This value is a direct indication of contaminants such as lignite coal, sulfides, and sulfates: all inorganic carbons that can cause issues in a firing. High sulfur content in a clay body is directly expressed by higher LOI values. Dark and red bodied clays contain higher levels, but high plasticity ball clays usually contain higher carbon content. The general rule of thumb: highly plastic ball clay fields are typically located adjacent to coal seams.
 
Historically, calculating LOI totals was based on a single firing of raw clay or other ceramic materials to 1800F/1000C. Often times material analysis were performed, and a LOI value was inserted to balance the totals to 100. Kaolin can have high LOI values due to the chemically combined moisture content; referred to as molecular moisture. The molecular moisture content of kaolin can run as high as 14% of weight, but kaolin is otherwise fairly free of inorganic contaminants. Ball clay on the other hand has little to no molecular moisture content, but can have inorganic contaminants  higher than kaolin. 
 
Calcining kaolin in order to reduce shrinkage in slip and glaze recipes is a common practice among potters. Many potters calcine kaolin to a bisq temperature which is not necessary: molecular moisture is driven off by 1112F/600C. This temperature is just prior to when combustion begins to occur in the kiln chamber. Inorganic carbons burn off from 1250 to 1750F (665-950C) which include various forms of sulfur: lignite coal and iron (disulfide) being the common contaminants. The temperature range for molecular moisture and inorganic contaminants is the basis for the Split LOI test. For this same reason, this test requires two separate firings to determine rather molecular moisture or inorganic carbons are being burnt off.
 
Test Protocols: field clay must be cleaned by the slurry method and debris removed. Then throughly dried and ran through an 80 mesh sieve. A finer mesh is required to remove remaining sand or large particles. 500 grams is required in order to detect small variables in either the first or second firing. Most scales used by potters are not sensitive enough to detect small variations in lesser sample weights. Samples for the second firing should be placed in a shallow form to protect shelves in case some fluidity develops. Do not add any other materials to your raw clay sample. Fire in oxidation, spreading material evenly in a shallow form on slow ramp speed.
 
The first firing is to measure molecular moisture and/ or organic carbon content. If properly cleaned, organic carbon content should be minimal. Fire to 1112F/600C with a short 10 minute hold to ensure uniform heat distribution. Upon cooling, weigh the test sample and note LOI loss. Fire this same sample the second time to 1800F/1000C with a short ten minute hold. You can fire the second sample as part of a normal bisq firing if you choose.  Upon cooling, weigh the sample and note the LOI loss separately of the first firing. The weight loss noted in the second firing is a direct indication of the inorganic content of the sample.The combination of the first and second firing is the total LOI for the material.
 
If you recorded high LOI loss in the first firing: your sample is kaolin or kaolinitic in composition. The exception would be ball clay with high organic content which usually presents as black or black streaks. Kaolin has much higher molecular moisture content than ball or fire clay. If your second firing recorded higher LOI than the first firing: then your sample is either ball clay or fire clay. Ball and fire clay have little to no molecular moisture content, but have low to higher inorganic carbon content. To some extent the LOI loss in the second firing can indicate the plasticity level. Highly plastic ball clay is typically located adjacent to coal seams with higher inorganic carbon content. Not conclusive, but higher second firing LOI values would warrant additional plasticity tests such as WOPL. ( water of plasticity) 
 
Additional information can be gleamed from the second firing as well. At 1800F/1000C, enough heat is present to produce color if appreciable amounts of iron are present in your sample. If nodules or fluidity occurs at bisq temperature: both would indicate a low fire earthenware variety clay. Nodules are more indicative of natural fluxes, fluidity is more conducive with low alumina content. Fluidity would then require the addition of high alumina kaolin be added to increase refractoriness. Finally if the sample appears very dark or black, and/or hard nodules have formed: this would indicate high levels of iron disulfide with additional sulfides from lignite coal. This kind of sample would produce blistering, bloating, or carbon coring if not fired correctly. 
 
 
Tom

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Thanks! FYI, the reason we usually calcine kaolin at bisque temps is because it's easy to just put it into a bisque firing, rather than doing a separate firing just for a small amount of kaolin. However it's nice to know that we don't have to go that hot if we do need to run a separate load, or can do it in the test kiln.

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7 hours ago, glazenerd said:

I developed this test primarily to test clays: you will not find it in text books- it is being introduced for the first time. 

Split LOI Test

 
Loss on ignition is a chemistry term, measuring the amount of organic/inorganic material released from solids, when they are heated to a temperature that is high enough to produce combustion. In pottery/ceramics, the definition is widened and application broader. LOI is applied to minerals such as silica, feldspars, talc, dolomite, and other commonly used glaze ingredients. In addition, LOI is also applied to clays, bentonites, plasticizers, and hectorites. 
 
LOI of clay is considered when trying to calculate the properties of raw clay or blended bodies. LOI for individual raw clay is an important value for judging the suitability for use in a blended body. This value is a direct indication of contaminants such as lignite coal, sulfides, and sulfates: all inorganic carbons that can cause issues in a firing. High sulfur content in a clay body is directly expressed by higher LOI values. Dark and red bodied clays contain higher levels, but high plasticity ball clays usually contain higher carbon content. The general rule of thumb: highly plastic ball clay fields are typically located adjacent to coal seams.
 
Historically, calculating LOI totals was based on a single firing of raw clay or other ceramic materials to 1800F/1000C. Often times material analysis were performed, and a LOI value was inserted to balance the totals to 100. Kaolin can have high LOI values due to the chemically combined moisture content; referred to as molecular moisture. The molecular moisture content of kaolin can run as high as 14% of weight, but kaolin is otherwise fairly free of inorganic contaminants. Ball clay on the other hand has little to no molecular moisture content, but can have inorganic contaminants  higher than kaolin. 
 
Calcining kaolin in order to reduce shrinkage in slip and glaze recipes is a common practice among potters. Many potters calcine kaolin to a bisq temperature which is not necessary: molecular moisture is driven off by 1112F/600C. This temperature is just prior to when combustion begins to occur in the kiln chamber. Inorganic carbons burn off from 1250 to 1750F (665-950C) which include various forms of sulfur: lignite coal and iron (disulfide) being the common contaminants. The temperature range for molecular moisture and inorganic contaminants is the basis for the Split LOI test. For this same reason, this test requires two separate firings to determine rather molecular moisture or inorganic carbons are being burnt off.
 
Test Protocols: field clay must be cleaned by the slurry method and debris removed. Then throughly dried and ran through an 80 mesh sieve. A finer mesh is required to remove remaining sand or large particles. 500 grams is required in order to detect small variables in either the first or second firing. Most scales used by potters are not sensitive enough to detect small variations in lesser sample weights. Samples for the second firing should be placed in a shallow form to protect shelves in case some fluidity develops. Do not add any other materials to your raw clay sample. Fire in oxidation, spreading material evenly in a shallow form on slow ramp speed.
 
The first firing is to measure molecular moisture and/ or organic carbon content. If properly cleaned, organic carbon content should be minimal. Fire to 1112F/600C with a short 10 minute hold to ensure uniform heat distribution. Upon cooling, weigh the test sample and note LOI loss. Fire this same sample the second time to 1800F/1000C with a short ten minute hold. You can fire the second sample as part of a normal bisq firing if you choose.  Upon cooling, weigh the sample and note the LOI loss separately of the first firing. The weight loss noted in the second firing is a direct indication of the inorganic content of the sample.The combination of the first and second firing is the total LOI for the material.
 
If you recorded high LOI loss in the first firing: your sample is kaolin or kaolinitic in composition. The exception would be ball clay with high organic content which usually presents as black or black streaks. Kaolin has much higher molecular moisture content than ball or fire clay. If your second firing recorded higher LOI than the first firing: then your sample is either ball clay or fire clay. Ball and fire clay have little to no molecular moisture content, but have low to higher inorganic carbon content. To some extent the LOI loss in the second firing can indicate the plasticity level. Highly plastic ball clay is typically located adjacent to coal seams with higher inorganic carbon content. Not conclusive, but higher second firing LOI values would warrant additional plasticity tests such as WOPL. ( water of plasticity) 
 
Additional information can be gleamed from the second firing as well. At 1800F/1000C, enough heat is present to produce color if appreciable amounts of iron are present in your sample. If nodules or fluidity occurs at bisq temperature: both would indicate a low fire earthenware variety clay. Nodules are more indicative of natural fluxes, fluidity is more conducive with low alumina content. Fluidity would then require the addition of high alumina kaolin be added to increase refractoriness. Finally if the sample appears very dark or black, and/or hard nodules have formed: this would indicate high levels of iron disulfide with additional sulfides from lignite coal. This kind of sample would produce blistering, bloating, or carbon coring if not fired correctly. 
 
 
Tom

Nice,

sounds reasonable, logical and very useful!

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Bill:

I sent this testing to Ron Roy and Tony Hansen a couple of months back for peer review. Ron stamped it and Tony is "taking it for a test drive."   A forum member sent me a sample of wild clay to test not too long ago. In the first pic the raw sample is on the left, results of the first phase LOI (middle)  and Imco Burgundy on the right for comparison (iron levels)  it was fairly plastic in the raw state, but extremely short after the first burn out phase: which means plasticity was derived from organic Ord humus ( black streaks in clay)  

In the second phase (in dish) the iron became apparent as did the calcite ( white granular)

 

IMG_0162.JPG

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3 hours ago, glazenerd said:

Bill:

I sent this testing to Ron Roy and Tony Hansen a couple of months back for peer review. Ron stamped it and Tony is "taking it for a test drive."   A forum member sent me a sample of wild clay to test not too long ago. In the first pic the raw sample is on the left, results of the first phase LOI (middle)  and Imco Burgundy on the right for comparison (iron levels)  it was fairly plastic in the raw state, but extremely short after the first burn out phase: which means plasticity was derived from organic Ord humus ( black streaks in clay)  

In the second phase (in dish) the iron became apparent as did the calcite ( white granular)

 

IMG_0162.JPG

I think it’s an astute informed method which likely will be useful to many and likely has reasonable precision for its intention. Nice work!

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