ASH GLAZES AND THE EFFECT OF COLORANTS AND FIRING CONDITIONS
ASH GLAZES AND THE EFFECT OF COLORANTS ANDFIRING CONDITIONSAPPROVED:Major ProcessorMinor ProfessorDirector of t'nent of ArtDean of the Graduate School
ASH GLAZES AND THE EFFECT OF COLORANTS ANDFIRING CONDITIONSVolume ITextTHESISPresented to the Graduate Council of theNorth Texas State University in PartialFulfillment of the RequirementsFor the Degree ofMASTER OF ARTSByJames Denny Jones, B. A,Denton, TexasJune, 1969
TABLE OF CONTENTSVOLUME IPageixLIST OF TABLESXLIST OF ILLUSTRATIONSChapterI.INTRODUCTION1The Problem and Its PurposeExperimental PlanDefinitionsConclusionII. PROCEDURE9Tri-Axial Blend MixturesFormulation of Compounds Excluding ColorSatisfactory Glazes with Colorants AddedSummaryIII.TESTING RESULTS19Base Glazes in Reduction FiringBase Glazes in Oxidation FiringBase Glazes with Colorants AddedClassification of GlazesIV.SUMMARY, CONCLUSIONS, AND RECOMMENDATIONS . . .BIBLIOGRAPHY. . . . . . . . .iii4146
LIST OF PLATESVOLUME IIPlateI.GLAZE 43 IN OXIDATION AND REDUCTION FIRING EXCLUDING UsingUsingMesquite in Oxidation FiringMesquite in Reduction FiringHackberry in Oxidation FiringHackberry in Reduction FiringGLAZE 43 USING HACKBERRY IN OXIDATION FIRING WITHCOLORANTS ADDEDGlaze 43 Using Hackberry inwith 5% Red Iron OxideGlaze 43 Using Hackberry inwith 1% Copper CarbonateGlaze 43 Using Hackberry inwith %% Cobalt CarbonateGlaze 43 Using Hackberry inwith 5% Vanadium StainGlaze 43 Using Hackberry inwith 2% Manganese DioxideIII.Oxidation FiringOxidation FiringOxidation FiringOxidation FiringOxidation FiringGLAZE 43 USING MESQUITE IN OXIDATION FIRING WITHCOLORANTS ADDEDGlaze 43 Using Mesquite in Oxidationwith 5% Red Iron OxideGlaze 43 Using Mesquite in Oxidationwith 1% Copper CarbonateGlaze 43 Using Mesquite in Oxidationwith h% Cobalt CarbonateGlaze 43 Using Mesquite in Oxidationwith 5% Vanadium StainGlaze 43 Using Mesquite in Oxidationwith 2% Manganese DioxideivFiringFiringFiringFiringFiring
PlateIV.GLAZE 43 USING HACKBERRY IN REDUCTION FIRING WITHCOLORANTS ADDEDGlaze 43 Using Hackberry inwith 5% Red Iron OxideGlaze 43 Using Hackberry inwith 1% Copper CarbonateGlaze 43 Using Hackberry inwith %% Cobalt CarbonateGlaze 43 Using Hackberry inwith 5% Vanadium StainGlaze 43 Using Hackberry inwith 2% Manganese DioxideV.Reduction FiringReduction FiringReduction FiringReduction FiringReduction FiringGLAZE 43 USING MESQUITE IN REDUCTION FIRING WITHCOLORANTS ADDEDGlaze 43 Using Mesquite in Reductionwith 5% Red Iron OxideGlaze 43 Using Mesquite in Reductionwith 1% Copper CarbonateGlaze 43 Using Mesquite in Reductionwith h% Cobalt CarbonateGlaze 43 Using Mesquite in Reductionwith 5% Vanadium StainGlaze 43 Using Mesquite in Reductionwith 2% Manganese DioxideVI.FiringFiringFiringFiringGLAZE 53 IN OXIDATION AND REDUCTION FIRING EXCLUDING ngUsingUsingUsingMesquite in Oxidation FiringMesquite in Reduction FiringHackberry in Oxidation FiringHackberry in Reduction FiringGLAZE 53 USING HACKBERRY IN OXIDATION FIRING WITHCOLORANTS ADDEDGlaze 53 Using Hackberry inwith 5% Red Iron OxideGlaze 53 Using Hackberry inwith 1% Copper CarbonateGlaze 53 Using Hackberry inwith h% Cobalt CarbonateGlaze 53 Using Hackberry inwith 5% Vanadium StainGlaze 53 Using Hackberry inwith 2% Manganese DioxideOxidation FiringOxidation FiringOxidation FiringOxidation FiringOxidation Firing
PlateVIII.GLAZE 53 USING MESQUITE IN OXIDATION FIRING WITHCOLORANTS ADDEDGlaze 53 Using Mesquite in Oxidationwith 5% Red Iron OxideGlaze 53 Using Mesquite in Oxidationwith 1% Copper CarbonateGlaze 53 Using Mesquite in OxidationwithCobalt CarbonateGlaze 53 Using Mesquite in Oxidationwith 5% Vanadium StainGlaze 53 Using Mesquite in Oxidationwith 2% Manganese DioxideIX.FiringFiringFiringReduction FiringReduction FiringReduction FiringReduction FiringReduction FiringGLAZE 53 USING MESQUITE IN REDUCTION FIRING WITHCOLORANTS ADDEDGlaze 53 Using Mesquite in Reductionwith 5% Red Iron OxideGlaze 53 Using Mesquite in Reductionwith 1% Copper CarbonateGlaze 53 Using Mesquite in Reductionwith h% Cobalt CarbonateGlaze 53 Using Mesquite in Reductionwith 5% Vanadium StainGlaze 53 Using Mesquite in Reductionwith 2% Manganese DioxideXI,FiringGLAZE 53 USING HACKBERRY IN REDUCTION FIRING WITHCOLORANTS ADDEDGlaze 53 Using Hackberry inwith 5% Red Iron OxideGlaze 53 Using Hackberry inwith 1% Copper CarbonateGlaze 53 Using Hackberry inwith %% Cobalt CarbonateGlaze 53 Using Hackberry inwith 5% Vanadium StainGlaze 53 Using Hackberry inwith 2% Manganese E 54 IN OXIDATION AND REDUCTION FIRING EXCLUDING ngUsingMesquite in Oxidation FiringMesquite in Reduction FiringHackberry in Oxidation FiringHackberry in Reduction FiringVI
PlateXXI.GLAZE 54 USING HACKBERRY IN OXIDATION FIRING WITHCOLORANTS ADDEDGlaze 54 Using Hackberry inwith 5% Red Iron OxideGlaze 54 Using Hackberry inwith 1% Copper CarbonateGlaze 54 Using Hackberry inwith %% Cobalt CarbonateGlaze 54 Using Hackberry inwith 5% Vanadium StainGlaze 54 Using Hackberry inwith 2% Manganese DioxideXIII.Oxidation FiringOxidation FiringOxidation FiringOxidation FiringOxidation FiringGLAZE 54 USING MESQUITE IN OXIDATION FIRING WITHCOLORANTS ADDEDGlaze 54 Using Mesquite in Oxidationwith 5% Red Iron OxideGlaze 54 Using Mesquite in Oxidationwith 1% Copper CarbonateGlaze 54 Using Mesquite in Oxidationwith %% Cobalt CarbonateGlaze 54 Using Mesquite in Oxidationwith 5% Vanadium StainGlaze 54 Using Mesquite in Oxidationwith 2% Manganese DioxideXIV.FiringFiringFiringFiringFiringGLAZE 54 USING HACKBERRY IN REDUCTION FIRINGWITH COLORANTS ADDEDGlaze 54 Using Hackberry inwith 5% Red Iron OxideGlaze 54 Using Hackberry inwith 1% Copper CarbonateGlaze 54 Using Hackberry inwith h% Cobalt CarbonateGlaze 54 Using Hackberry inwith 5% Vanadium StainGlaze 54 Using Hackberry inwith 2% Manganese DioxideviiReduction FiringReduction FiringReduction FiringReduction FiringReduction Firing
PlateXV.GLAZE 54 USING MESQUITE IN REDUCTION FIRING WITHCOLORANTS ADDEDGlaze 54 Using Mesquite in Reductionwith 5% Red Iron OxideGlaze 54 Using Mesquite in Reductionwith 1% Copper CarbonateGlaze 54 Using Mesquite in ReductionwithCobalt CarbonateGlaze 54 Using Mesquite in Reductionwith 5% Vanadium StainGlaze 54 Using Mesquite in Reductionwith 2% Manganese DioxideviiiFiringFiringFiringFiringFiring
LIST OF TABLESTablePageI.II.III.IV.Analysis of Tri-Axial Blend13-14Analysis of Base Glaze Color23-24Analysis of Base Glaze Surfaces26-27Analysis of Base Glazes withColorants Added30-31ix
LIST OF ILLUSTRATIONSFigure1.PageTri-Axial Blend11x
CHAPTER IINTRODUCTIONThe final step or procedure in producing a piece of pottery is that of applying a glaze and firing.It is the glazethat gives a ceramic piece its most dominant characteristicbeyond the basic shape.Although there are many types ofglazes, they are all basically nothing more than a thin glasslike coating fused to the clay surface of the pot by the heatof the kiln (2, p. 161).Glazes may be categorizedfollowing four ways:according to Norton in the(1) transparency, (2) surface, (3) color,or (4) composition (3, pp. 229 and 230).Although the class-ifications of glazes vary, all contain certain oxides in common.To better understand this common basis to all glazes,one should think of a glaze as a completed melt, containingonly oxides as they have resulted from the combining and melting of raw materials (4, p. 78).For better communication, itis necessary to set up a method of recording the amount ofthese oxides found in a specific glaze and to identify whichmaterials will yield these oxides in a given quantity.is done by means of the empirical formula.This"The empiricalformula is a method of representing a finished or melted glazein terms of the relative amounts of the various oxides whichare present" (4, p. 78).The empirical formula is used to1
show the relationship between oxides in a glaze and the organization of the oxides into three specific groups.groups are known as RO, R2O3# and RO2.TheseEach group containsoxides that perform the same or similar function in the creation of the glaze.The RO, or base group, acts as the fluxing agent.Themiddle group, R2 3» is chemically neutral and assists in thereaction of RO on RO2; it does not act as a flux yet it influences the melt of the glaze.R02» the acid, containsmainly silica and is the refractory part of the glaze.Al-though glazes may contain many materials, all the elementswill serve one of these three group needs in a glaze.Although it is possible to calculate precisely the composition of a glaze so that it will meet a specific need,most potters work in a less scientific way.Through the ages,many of the most beautiful glazes have been created in a trialand-error manner.Some materials contain the necessary glaze-making oxides in varying amounts so that it is not possible -to calculate exactly what the glaze will be.One of thesematerials which may be used to produce outstanding glazes isthe ash of various vegetable materials.The Problem and Its Purpose1The study being undertaken wasto ascertain the effect oreffects of different firing conditions and colorants on glazescomposed of wood ash from two trees indigenous to Texas.The
problemwas;divided into two parts:first, to identifythe best mixtures using the selected vegetable ash; second,to alter successful glazes with set percentages of colorants.The main objective of the study was to evaluate findingsresulting from the variation of elements, firing conditions,and colorants used and to select successful glazes.Experimental PlanThe study was limited in three ways.A limitation wasset on the number of raw materials used in producing glazes.Ash, feldspar, and whiting were the raw materials chosen because their component parts are known to produce satisfactoryglazes."A suggested starting point for a stoneware ash glazetest would be 40 parts ash, 40 parts feldspar and 20 partswhiting" (2, p. 167).basic variant.Of these three ingredients, ash was theBoth types of wood were collected and reducedto ash by burning in an open pit."Ashes contain alkaline inmore or less soluble form together with silica, alumina, andsmall percentages of other elements" (5, p. 160).The woodcollected for the study was obtained in Denton County andeach variety was taken from one tree or one group of treesrespectively.the ash.This step was taken to insure uniformity ofAshes vary widely in composition and even the ashfrom two examples of a given variety of tree will vary, depending on the soil in which they grew (4, p. 188).The second limitation was set in the different types ofash to be used, mesquite ash and hackberry ash.Another
variant was established in the firing conditions with alltesting conducted in both oxidation and reduction firings.The third and final limitation was the number of colorants tobe added to successful glazes.The colorants chosen were rediron oxide, copper carbonate, cobalt carbonate, vanadium stain,and manganese dioxide.DefinitionsComponents—In the introduction to the study it was citedthat all glazes have a common basis.empirical formula of RO,anc*R02*This basis being theT ie c o m*P o n e n t s offeldspar, ash, and whiting combined account for these necessities.Variation of the proportion of the components affectsthe character of the glaze.Feldspar is used both as a fluxing agent and for itssilica content.Feldspars are considered a cheap source ofglaze flux and have the additional advantage of being nonsoluble (2, p. 211).The feldspar used in this study was apotassium feldspar with the theoretical formula ofK20-AL203-6SiC 2; this was purchased locally."Whiting, calcium carbonate (CaC03), is the major highfire fluxing agent, although it has a minor use in bodieswhere a small amount will lower vitrification temperaturesjand reduce porosity" (2, p. 218).Two different wood ashes were employed in this study.Hackberry (Celtis occidentalis) and mesquite (Porsopisglandulosa) were the two plants chosen for the study because
both were plentiful in the local area.Hackberry thrives invarious regions, but more commonly in rich soil.Its wood isheavy but soft and weak, and decays rapidly when exposed(6, p. 27).Mesquite is found mainly in hilly pastures westof the Trinity River.Mesquite wood is heavy, hard, close-grained, and durable in soil (6, p. 240).Firing conditions.—In this study all glazes were testedin two firing atmospheres.All glaze samples were fired inboth an oxidizing atmosphere andareduction atmosphere.The oxidation firing was conducted in an electric kiln wherethe atmosphere was static and neutral.An oxidizing fire isone during which the kiln chamber retains an ample supply ofoxygen.For this to take place, the combustion in the firebox of a fuel-burning kiln must be perfectly adjusted.Anelectric kiln will normally give an oxidizing fire.Reduction firing was done in a gas kiln.The term re-duction fire as used in this study refers to the chemicalreaction by which, under great heat, free carbon in the kilnwill unite with the oxygen combined in ceramic compounds(2, p. 239).Both atmospheres mentioned above were used in firing theseash glazes because of the differences that can be obtained."In oxidation most glazes made with ash will tend to be somewhat tan in color, due to the small amounts of iron normallypresent in the ash.In reduction the prevailing color will begray or gray-greeh"(5, p. 162).
Colorants.—Five colorants were added to the satisfactorybase glazes so that the variation might be observed.Red ironoxide (Fe203) in glazes produces colors ranging from amberthrough tan to deep red brown or gray to green, depending onthe quantity of iron and the atmosphere of the kiln.Betweenfive per cent and ten per cent by weight of iron oxide shouldbe used (1, p. 192).Copper carbonate (CuC03) has been usedsince antiquity to produce colors of blue and green in glazes(4, p. 130).In a reduction atmosphere it also produces reds.A suggested amount of copper carbonate to be used would betwo per cent by weight."Cobalt carbonate (C0CO3) is themost stable and reliable glaze colorant.It gives a similarshade of blue in almost all types of glazes and under variousfiring conditions" (4, p. 131).Cobalt is the most powerfulof coloring oxides and for this reason, only one-half of oneper cent by weight is needed for color.Vanadium oxide added to a base glaze will produce ayellow color.Vanadium is usually used in glazes as a stainwhich is prepared by combining vanadium pentoxide, (V2O5),with tin oxide (4, p. 133).Because there is only a smallamount of vanadium oxide in vanadium stain, a larger percentageis needed for color."Five per cent will usually give a weakyellow, and eight to ten per cent, a strong yellow"(4, p. 133).Manganese gives a brown or purple color to a base glaze.Manganese dioxide (MnC 2), compared to cobalt or copper, is a
weak colorant, and 2 or 3 per cent by weight is usually required to give a pronounced color (4, p. 132).ConclusionChapter I has given the reader background informationon the formation of glazes and their classifications.Theproblem undertaken in this study was stated and related information to the problem was defined.Chapter II will be a step-by-step recording of procedures used in solving the problem.Information, terms, andprocedures covered in Chapter I will be directly applied tothe problem in Chapter II.
CHAPTER BIBLIOGRAPHY1.Kenny, John B., The Complete Book of Pottery Making, NewYork, Greenburg, 1949.2.Nelson, Glenn C., Ceramics: A Potter's Handbook, NewYork, Holt, Rinehart and Winston, 1960.3.Norton, F. H., Ceramics for the Artist Potter, Cambridge,Addison-Wesley Publishing Company, Inc., 1956.4.Rhodes, Daniel, Clay and Glazes for the Potter, New York,Chilton Book Company, 1957.5.', Stoneware and Porcelain: The Art of HighFired Pottery, New York, Chilton Book Company, 1959.6.Stillwell, Norma, Key and Guide to the Woody Plants ofDallas County, Dallas, Boyd Printing Company, 1939.8
CHAPTER XIPROCEDURETesting in this problem was divided into two steps.Stepone was the formulation of compounds excluding colorants andstep two was the testing of the satisfactory glaze formulaewith the addition of colorants.Because the major variant of the study was wood ash, itwas necessary first to collect and to process the two differentwoods.As mentioned in Chapter I, the two woods selected weremesquite (Prosopis glandulosa) and hackberry (Celtis occidentalis).These plants were chosen for two basic reasons:bothare indigenous to Texas, and both are readily available in thelocal area.Mesquite wood was gathered in Denton County near the cityof Lewisville, Texas.collected.Both dead wood and green wood wereAfter gathering, the wood was reduced to ashes byburning in an open pit.The hackberry wood was collected inDenton County in Denton, Texas.Once again, both dead woodand green wood were gathered and reduced to--ashfes by burning inan open pit.iIn processing the ash of each wood, it was decided thatneither a washing nor a decanting procedure would be undertaken.This decision was made in consideration of the fact that each
10washing of an ash removes alkalies and makes the glaze lessfusible (3, p. 161).It is possible to use wood ash in aglaze without washing.This unrefined ash often produces afinish with a more mottled and interesting effect than thatproduced with refined materials because of the particles andunburned matter removed by washing.Both the mesquite andthe hackberry ashes'were passed through a 30-mesh screen to remove any lumpy or large unburned pieces of material.Afterthis one step of processing, the ash was weighed out directly for the glaze."The general practice is to first run thedry ash through a very coarse sieve to remove unburned particles.The ash is then soaked in water that is decanted andscreened through a 60-100 mesh sieve and dried" (1, p. 167).In this type of processing, the glaze is more likely to besmooth and refined in character.Tri-Axial Blend MixturesThe system chosen for determining combinations of thethree glaze ingredients was by tri-axial blending of thematerials.To calculate the combinations by use of a tri-axial, an equilateral triangle diagram was drawn with pointsA, B, and C.Each point on the triangle represents 100 gramsof one of the materials being used.In this case, A repreesents ash, B represents feldspar, and C represents whiting.This is shown in Fig. 1.On line A-B of triangle ABC tenequal units were marked off by points.This was also done
11on lines B-C and C-A respectively.Next, lines were drawnparallel to lines A-B, B-C, and A-C from each of the pointscrossing at a total of 66 points on and within the boundry oftriangle ABC.Each point made by the connecting of lines wasgiven Arabic numbers from 1 through 66, denoting the combinations of the three basic raw materials to be used.In thisway A was identified as number 1, B as number 66, and C asnumber 56.100 A100 C57585960616263A—AshB—FeldsparC—WhitingFig. 1—Tri-axial blend64100 B
12As stated, A represents 100 grams of ash, B represents100 grams of feldspar, and C represents 100 grams of whiting.The midway point of line A-B represents one-half or 50 gramsof ash and one-half or 50 grams of feldspar.Other pointson line A-B will contain different amounts of ash and feldspar.If a point on line A-B is closer to A than B, it willcontain more ash than feldspar, if closer to B than A, itwill contain more feldspar than ash.The composition of apoint on the inside of triangle ABC will depend on its distanceaway from the points at the corner.Mixture 26 will contain20 per cent of whiting since it is eight spaces removed fromC, and 40 per cent or grams of feldspar since it is sixspaces removed from B.It will also contain 40 per cent orgrams of ash since it is six spaces removed from A.Similarly,the composition of any ot
glazes. "A suggested starting point for a stoneware ash glaze test would be 40 parts ash, 40 parts feldspar and 20 parts whiting" (2, p. 167). Of these three ingredients, ash was the basic variant. Both types of wood were collected and reduced to ash by burning in an open pit. "Ashes contain alkaline in
12 Ash glazes 89 13 Celadon and Copper red glazes 95 14 Drippy glazes and Chun glazes 101 15 Crystalline glazes 109 16 Shrink and Crawl: Lichen glazes 117 17 Volcanic, Lava or Crater glazes 125 18 Spotted glazes 135 19 Metallic glazes 141 20 Layering glazes 145 Conclusion 147 References 148
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Egyptian glazes b. Lead glazes c. Ash glazes d. Salt glazes e. Slip glazes f. Feldspathic glazes. 3. Basic oxides and their function in glaze. forming a. Oxidation and the oxides b. Glaze oxides c. Function of oxides in glazes d. The process of glaze melting in kiln. 4. Ceramic Oxides a. Aluminum Oxide A1203
alkali glazes, ash glazes and feldspar glazes. Furthermore, stoneware engobes and a few earth-enware glazes are tested. The latter is included to point to possibilities for other function areas than those covered by this project. Of the selected glazes, only feldspar glazes are in fact suitable for industrial production. The
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Copper Vary Ox. 0-2.5% In various glazes except those high in barium or mag-nesium. Best in glazes opacified with tin or titanium. Cobalt Vary Both 0-2% In glazes opacified with titanium, or containing rutile. Apple Green Chromium Vary Both 0-2% In various glazes without zinc or tin. Good in al-kaline glazes with zirconium opacifiers. Also use
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