THE DEVELOPMENT OF A YELLOW GLAZE FOR TERRA COTTA DONALD BURGESS ATWELL THESIS FOR THE DEGREE OF BACHELOR OF SCIENCE IN CERAMIC ENGINEERING COLLEGE OF ENGINEERING UNIVERSITY OF ILLINOIS 1922 Digitized by the Internet Archive in 2015 https://archive.org/detaiis/deveiopmentofyeiOOatwe /a So as. LAP / 9 sa Ai 3 UNIVERSITY OF ILLINOIS i9i22. THIS IS TO CERTIFY THAT THE THESIS PREPARED UNDER MY SUPERVISION BY Donald B u r g e s s Atwell ENTITLED IS APPROVED BY ME AS FULFILLING THIS PART OF THE REQUIREMENTS FOR THE DEGREE OF P.? Science HEAD OF DEPARTMENT OF 1 ■ I ■ ■ , '‘ij^' t fl ' "" '^' ' '" >••1 ■ ' iX. ,< w< ■ < \. ^ # ^,>;-:i',', *%« ■?■> -V^ ?\ ... I ft '* <•' '"ft . & , V ”, >^-»-' ;,r^v.r.=,'V-^ 1 iv. h .i*- i.., '^'i.i( 5^ 5 XV • . . ., ^ »jit' ", - ' *<«<* -* I '*V'^ -f •" ifc,“ „. • •■^\' r*’*l "i, / 3 !; 'W *. . -.„ :r' . IF ■*. ^ . ■ t y»' "Xs|; j-ji:’’* n'. - t J^‘ V -^»U ^v'\, -‘i r, x: £5 Yatef.’tivS-wu^ ai^idH-v ^ht i^iF...fe i..;', 7 ft: ■#'!<,( ■ a/FcTM tH b r S'— * ^ M.. I 0S‘ ' if f> ~ i'^i U 7 7 t m , \ ' ‘ ,» ’>: t'.*, fv n'lfiU-* •'«'; 4f.‘ 4'V'iii^7Af‘''^’f^ 7*^* '*S|M '•■ • ‘w r’ tu m'M\ * ' rf"' i 7 4; ■ :71i * ■> i f • > TABLE OF COITTEBTR Part One Page I. Introduction 1 II. Biscuseion of Previous Work and Literature 3 III. Exo ^=ri mental Method Emnloyed 6 IV. Body, Slins and Glazes Investigated 7 V. Blending, Dimoing and Firing 11 VI. Results 13 Table No. 1, Results 14 VII. Conclusions 15 Part Two I. Changes in Glaze Comoo sit ion l6 II. Preoaration, Blending, Aopli cation, Firing 17 III. Results 18 Table No. 2 19 Table No. 3 20 Graoh Firing Schedule 21 IV. Summary 22 V. Conclusions 23 , ■ (iir’ 1TO v' i ■' -f ‘X'^' r;-v.-|« ' ■ ■ j rfc & ^ ■•' ^ -"L k,;-' r'-W"tir7' /’-s . ;■ 'v''-^ •'JFP r- y^ j * *4 )i.'A>^‘J •■ V « t !% u . ’*\ t _ . » j if* .' 1 . ',: ■‘' d |'•%4|i'■/ ■: '/:'^' 4' 'ifi' ''ii Jv< tim'' *'’"i '■ ’■ ' J‘Y'-’‘* 3*5^. .'- ■ v.,-» St'V "«S^ ’> k - k < .’ •^•-StuP^ • *M.wpi -j*.v e^'!’''?i'y'*^’»% srjnj I'V k#.J5^25«|iftWllliflC‘ * .'i >'i'^ ' -i ,«r-': >.uk4s> ''l\;>»'^j;k!fV'-* ii:..',r.; '’'■ •■»6.<'Arf('i'6ap;. . -i,,, ■• nr^. m *t,us ^mmMmm. ^KrLJWJf ' .< m ~v. ^ rmr >r.\rKM v •« <. '-'it j ‘:-^- i-f 1‘>J ' • i *-9 \ . • ■ j ‘ ■ <*''•/ A^a: ' i ', •; -4' ‘-irM i': I y .,.■.■/■■ • 4 ' I** ifVi ' I'd r3 ■'• , . ■ ( '’■' v-ftTT- ._«•- '* The Development of a Yellow Glaze for Terra Cotta Part One I I nt roducti on In develoning a yellow glaze for terra cotta there are three things to con sider. A glaze for such use must mature well at the cone to which terra cotta ware is burned, which is usually about Sager cone five (5’)» It must develop the desired gloss and be free from erazing, pinholing, feathering and all glaze ■'defects at this cone , The glaze to be useful as a terra cotta glaze, must be such that it mil mature properly, without defects, when applied on a green terra cotta body over a slip which has been previous- ly applied. A terra cotta cla;^^ mix does not burn to a v/hite, and because of this it is necessary to use a white opague slip be- tween the glaze and the body so that the color of the body will have no effect on the glaze colors. The use of the coloring oxide is very important. The col- oring oxide should be such that it will nro :^ce good yellows which are clear and of such a strength that a aeries of shades may be obtained by variations in the amount of the coloring oxide used. The coloring strength of the oxide has a bearing on the nracti cabi li ty of its use commerci ally, for if excessive amounts have to be used to nroduce the desired denth of color in the glaze it may not be economically practical to use it as a pig- ment substance. Summarizing, my objectsrof research are: 2 1. To develoT) a glaze which, was suitable for use at Cone fi ve (5) together with a slip on a green body. 2. To secure a combination of glaze and coloring oxide to produce a yellov; which would be satisfactory from the color standpoint and be economically suitable for use as a glaze for terra cotta ware. i!^?*t;j9P0Ks^.^«'x:ii^Shffei^^;iiit«c»s^^ «aasf-. x;- y . ■+ 'f- ■ 4 f In ' ->i 'V - V ' '-fh LI I’ <.f ,'.<*'■ I '• J> ■s;'^ .i^-,.-., • .• :P '.rro , ^ H '’■ ^ j •!?> j' s * ' 'ii #v j: 3t^ ^ ;’..avm:, ■ Sj- ' ■',■ ■, i i3L ■P Hi • ■'’** '• ’ £ ' ■>' ■'' 1 . -t.,- V * " % . ' - ,>• '.•Vpi<‘->?^^ ,*V #* -4 ' * ■'*’■>• V^:' ifi.lfjp C T.t V V . 4 '^HfUrfU'r^l i ‘ _. ■ fe.: .v.'; ' ■,.:■"» ■ '■. ^•^' ' -' ir' ^'" l' 'V/, ' a ,..'t *0 ■ ‘ h. m- i 'i .. »'■: li! .■■ K' »MP -V. ^ iH'*' ^■'v'SvKl “ .*♦ ?^5r> ,.^ V V V'l'^ .. iW'X' ^L " ,4',:.- ' 'iiii FI 1/4 .i''^' -'v ■ 5 . , ,>i 3 . ■ :!^*T 'H 1 ^ . 'V -A»-, 4’. >■ tA ■! r > ' »»’ ■ . hwm-- 3 II Discussion of Previous ’^Vork and Literature. There seems to he pretty close agreement as to the yellow- producing oxides and pigment materials in the various authorit- ative hooks on the subject of glazes and ceramic colors. The range of materials for the production of yellow colors in glazes, as obtained from the various sources includes uranium oxide, iron oxide, antimony oxide, titanic oxide, leukonin, (sodium antimonate) tungstic acid, molyhdi c oxide, and a coloring fritt made uo of uranic nitrate fritted with feldspar. The various references and subject matter from them are as follows: 1. R. Fainbach- "Pottery Decorating". According to -^-.ainbach, very handsome nure yellows are ob- tained by the use of antimonic oxide in a white glaze in the nronorti ons of five to ten per cent (5-10.^^) oxide and ninety to ninety-five ner cent (90“9?^) glaze. Ke also states that ferric oxide and uranium oxide develop yellows, the ferric oxide also being used v.dth antimony oxide for procuring reddish or brovmi sh red yellows. He is also the authority for the state- ment that very handsome yellows have been obtained with silver, but this, obviously, is too expensive a material for use as a coloring oxide in a terra cotta glaze. 2. A. B. Searle- " Ceramics Industries Pocket Book". In his list of'colors used in pottery, glazing, enamelling and glass-staining", Searle lists the oxides of titanium, antimony, iron and uranium as being yellow-nro ducing oxides. 4 3. Emile Bourry- ’’Treatise on Ceramics Industries”. Bourry states that the oxide of uranium gives a yellow in an oxidizing fire. Ke also states that titanic acid develops yellows. To use his words; ”In glazes it (titanic acid) gives only yellow tints, due, partljr at least, to the iron that raw titanic acid always contains in commerce.* He is authority for the statement that pure iron oxide develops a good jrellow, although it tends toward a brown at high teraperatxires. He lists uranium oxide as a good yellow-producing oxide, except in the presence of lead, where it turns to an orange, 4. Taxile Doat- "Grand Feu Ceramics”. the authority for the use of nitrate of uranium fritted with feldspar as producing yellows is found here. Doat also advocates the use of uranium oxide for 3 ?” 0 llows, as well as oxide of iron for slightly brownish yellows. 5. Chemical Abstracts, AX, 93; ii'ew Yellow Color''- Vnon. According to this article, aerium phosphates have been used to develop birilliant yellows. 6. Notes on Ceramics 3. I found in my Ceramics notes a statement as to the use of tungstic acid* and molybdio oxide in. the presence of manganese for the development of yellow glazes. 7. Report of German Cera-iiic cociety, Dr.FurJ:. Reference was made in this report to the use of cerium oxide for the development of yellow glazes, no authority being given for the statement. ♦. Hertwig, Sprechsaal, 49 i 1845-1846 (1903), Abstract in the 1 • V iw-., , . Si’ ' %i » , • -U,. . ^ -^y 71 j •:■ It ' i V- 1'* *> » iT * . ; 'H Aft ty f V / I v^5ffP riM ■ 1 . i ~ : ' .( '1 * - X, -tm-^.9 ■'I a 'Ut :'-J ffS;'' ' -t . O’C f ■ i. . ' V p • 'j 7 y.-.tiv ‘hi> / w ,1 . f 'vit^ ■ i -t. ; 3. 0 Vv^-'V Wk lA, !•!- 7 7 ' 7 ;J ;'l ‘■I ,. h'^ f.^p, .'1 »• < ..-if' ,r ■.» '.I . _ r'l^.if : f *■ ’ ‘- >r fW'’ - ■ vvki ' *>( *Afi/ Jour. Soc. Chem. Ind. Jan. 30 (1904) pg. In a reducing fire yellow and orange shades with the use of tungstic acid. 8. Kertwig-Sprechsaal 49; p.l20. Cerium phosphate is used for the development of hrilliant yello’"s, according to this authority. 9., Hermann A. Ce ger, Collected Writings. Seger uses titanic acid in the development of hrilliant yellows in underglaze colors at lov/ temperatures. Ke makes the statement that the yellow color may he due to the presence of iron as an impurity. Uranium is also used hy f^.ger for the development of lemon yellows. With the use of uranium the necessity of avoiding reducing conditions becomes naramount. 1 0. Frank H, Riddle, "The Coloring Power of Uranium Oxide in Glazes of Various Comnositi ons. T . A.. C. S. , Vol. 8. The statement is made that the coloring power of urani’jm oxide is very great, as little as .006 equivalents producing a decided yellow. 11. Farl T. Montgomery- "Study of Underglaze Colors with View of Determing the Most Insoluble and Hon-Volat ile Underglaze Color Comoosition. T . A. C. S. Vol. 13» Montgomery finds that yellov;i sh grays, yellomsh blacks and yellovdsh greens are develoned mth uranium oxide. The color was lorepared as a fritt. The higher members gave the colors noted above. There i s no reference in this to there being any reducing conditions in the burn. 4 "I T;! ^ Vi*' »tt=; I I .T ! ;i' ■r i i 6 III Experimental Method Employed. The method of procedure in the work consisted of the following steps; (a) Selection of a hody material "which would closely ap- proximate the hody actually used in commercial hody as t o gen- eral behaviour. (h) Selection of a suitable white slip for use in masking the color of the hody, being used for application on the green hody. (c) Selection of a glaze suitable for ap"olication over the white sli"0 on the green body. ( d) Consi deration and investigation of the coloring oxides which are thought to be, and have been reported to be yellow- producing oxides, together with a consideration of the proper "oroportions necessary for incorporation v/i th the glaze to produce satisfactory shades of yellows. _ '^^:>‘^'^^ ‘ ' f '■a" ' *ir ‘ -lit ', V* -0 -H,rh' Iri p^T^lvh<‘ )t' ',*» •.-.if».:''^^%^;'iti..' "O' r»? * ?-• ff' »' ’■. • ;' % Mr "/<•' S*^, _ ':- v' fi-fr I ^ * _■- ,r 'r. ^ y* ' !. Wl IE HS .' lAijWr ,\- iiffi . .. *S ■' .’V- _Ji 'i#' SiSli'A'i. , . ^U«r ‘^' * - ifV U'-' V . Vi;- ■ ?i«t ’ ‘Me-' ^o': !fl^ ' \:li~‘l Jf A - jSkavu i.. i'^’ WJ.- ' ^ »■ ,' -.■ ■ ■' . ■■ fi, ■ j<> *;'T ■ ■■ * 27 -r(- .■ 4 m i ■ ' ' -.* ’ . * '7 ■ ■' '‘.''li^-"’ '' \'v . ,'Aa ' ' ■ •= ■ f ■ ■V'tv ^•; .!<• - . SJC.V, ? i-. ‘ t'Tffr' - - ?,S 57 , n »^-7 fT^, ^ ‘V j»Hii -.'/l. ,l| ■'«>» . ■*- '.' 4 , . ;^.« , -ii, •;. •■«< t .'. C’ .l^’l 'M f ., 7 . U* :4 ti '"7 -'A :%A0mT':''i '* .,<.'A'' >1 ..■: .* ■■' i** ‘',‘ C: 'f ,•. . J as a. ' ■. '■ '• ' 'J"--* ■■' ■‘7^.7-^^ .'r'-H m A '-'^ ’ 7^1 7 IV Body, Sli-ps and Glazes Investigated. 1. Body. The body used was made of Bloomingdale Stoneware clay. Preparation of the body consisted of grinding in a v/et pan and forming briguettes about three -fourths of an inch thick and two inches wide by four inches long. These were formed in a small brick auger machine by the use of a suitable die, the column run out being cut to the desired m dth of pieces. These were air dried and then dried in a steam-heated rack drier. 2. Sli'os. The slips used v/ere a typical terra cotta slip and a vitreous white slip as follows: (a) Terra cotta slip English China clay Tennessee Ball clay 10 % Feldspar ^ 0 % Flint 2 ^% (b) Vitreous white slip Cornwall stone ^ 0 % English Ball clay 1 ^% English China clay 20^^ Boric Acid 2 % Flint 1 % Calcium Carbonate 2 % Barium Carbonate 2 % Magnesium Oxide 1 % The nreparation was the same for both slips and consisted merely of grinding wet for three hours in ball mills and lavming through a screen of 140 meshes to the inch. #;:?. ^ '■ *' -■• - t»:tv n;iL ’•.«,“* '■*• ‘ *’ . ■ t »•■' ' ,' • ‘/ o/‘(C y ;is.t N- • ' U; n ^ ^ n' 4 A, . f ’ ;’ ' i/-riS ^5 • , .■ '■■ ■ -■ ' .■■ ‘->V r ‘ t - ■■ . ;(•.'' V: ' • ",'•' ^ ,. ’ r,j.' y^ .__ |^>, ... . . -* • t . -■ I ft ■• ' •* sjsxSf^^i ^ - ■..•^.-C?'^ V>'^!- 'Wl*. , - ■ v*-.|? W ' i \. ' I? •-i.v '( * » ■‘V '■ '•J. ■l'*: :'',i, ! *:ft«t(4'tat'‘ n-rs‘;--^^^ ■ fn.1' 1 ^ , M-j’a> •;'.», ' ^f- .'' ■»'■'. ' • i’|.' .,. - t-v. ;S ‘ it;t*!,^«.^’/.,_ / j '". ‘v*' .. 'i*: ■ si.'^ 'w* •■=»A 4 i r' i" ift i v',,Wi ^;«^i5'«.5iu ■-<«■' «« ‘;,C^ ;,«■ ■ ■' 'f #':''5?r ■ -:4 ;t| .. •? ,M, , i * -. _, ;• . .’I 9 «ii f .-.P^*-,'-- ;, •?.'■'.! ^ ^ '( h 'jLi^^ JM . * V . ' ^.. 2 ^ . '•A -.s' * .-X ii! ■ T |T 4 L» nj ^ «U. J ' •-■: ■ a’.'*. ' i'. '•■ . c^*] .t r-* Tx*? 'wf ?5wx.'' > /.k^;||’.M 0 '^- '■'•■ ^ ''® 8 . Glazes used. Two glazes were used, a fritted glaze and a bristol glaze: (a) Fritted Glaze: Fritt: - Y/hiting 35 uarts Feldspar 5^ parts Borax 57 parts Flint 5'^ parts Boracic acid 1 part Ceranic Formula: .3 .35 cao .283 AI 2 0 ^ . 2 K 2 O .31 B^O^ .15 Na20 (b) Bristol Glaze: Ceramic Formula: . 27OK2Q .234 ZnO .396 CaO ,100 BaO • 55 AI 2 0^ G1 aze - Fritt 160 parts White lead 77 parts Feldspar 5^ parts China clay 21 parts Flint 44 parts 3.0 SiO^ 3-3 Si02 Batch weights, figured on the basis that the coloring oxides renlace like amounts of CaO. Extreme .005 150.2 Feldspar 18,9 Zinc Oxide 39*1 Calcium Carbonate 19*7 Barium Carbonate 51.6 Raw clay iy.9 Calcined clay 67.1 Flint (.00^ Equivalents of coloring oxide). Extreme .10 150.2 Feldsnar 18.9 Zinc Oxide 29*6 Calcium Carbonate 19.7 Barium Carbonate 51.6 Raw Clay 17*9 Calcined Clay 67.1 F lint (.10 equivalent of coloring oxide). 4. Biscuited Tile Trial Pieces. Trial pieces of biscuited tile with the anplication of glaze on them were run to assure a knowledge of the various col- ors developed, in case the green oieces should not develop pronerly, 5 . Oxides used and their source (a) Leukonin SbOj* THgO) Introduced as such. (b) Cerium oxide (Ce02) Prepared by igniting basic ceric nitrate strongly. (c) Ferrous oxide (FeO) Introduced as ferric oxide (F 620 ^), pure. ( d) Uranium oxide (UpO^) Introduced as sodium uranate ^ (Ua2 O5 H^O) (e) Tungstic acid (K WO ) Introduced as such. 2 4 (f) Molybdic oxide (MoO^) Introduced as such. (g) Uranium Ui trate(U(lI 02 ) nt reduce d as such. (h) Manganese dioxide (MnOp) Introduced as such. 11 Blending, Dipning and Firing. 1. Blending. In 'both the fritted and the hri stol glaze the two color extremes, .00^ equivalents and .10 equivalents of color oxide present, were prepared and the intermediate colors prepared by blending these extremes in the oroper proportions figured in dry weight of glaze. All blending was carried out on the basis of the weight of dry glaze oresent in the glaze mix. This was found by weighing a certain known amount out in a dish, drying the glaze, weighing again and calculating the weight of dry material in one gram of wet material from the data obtained. Samnle Calculation for Blending. (a) Determination of dry weight. 1. Extreme .00^ equivalents coloring oxide. Weight of beaker and glaze slip -147.5 ” ” " and glaze slip dried 141. Igm. ” ” ” alone 1 36. Igm. Weight of slip 147. 5 “^36.1 11.4 gm. ” ’• '• dried 141.1 136. 1 5.O gm. Then 1 gm. dry 2.28 gm. wet glaze slio. 2. Extreme .10, calculated similarly, gives: 1 gm. dry 2.71 wet glaze slip. 3. The method of blending i s by the position of the glaze desired in reference to the two extremes as shovm below. O 0 0 It mil be noted that glaze .04 for instance, is seven (7) divisions from extreme .005 and twelve (12) ■y \ IliJM 12 divisions. The calculations , then, for making up the glaze are as follows: 50 X 12/19 X 2.28 72.0 gm. (.005 extreme) 50 X 7/19 X 2.71 4 - 9.9 gin* (.10 extreme) 2 . Dipping. Both the si ins and the glazes were dipped. The slip was brought to a specific gravity of approximately 1.5 as this is the most workable v/eight for dinping. The glazes were applied by dinning after the slips v/ere dinped, the specific gravity being the same as the slins when pieces were dipped. 3. Biring. The burning was all done in one burn,, that is, the body, slip and glaze were all burned, at one lurn^ The Time Temperature Schedule for the burn is shown in Graph ITo. 1 . Care v/as exercised to have an oxidizing atmosnhere in the kiln at all times, and ample time was allowed, at the end of the burn for the purpose of ’’soaking”, or equalizing the temperature over the entire kiln. Cones four and six v;ere placed in the saggers to indicate the heat treatment and cones three, four, five and six were used as sight cones. The burn went to Seger cone 5 * 9 « p.* < --^^1 13 VI Re suit s. 1. General. (a) The sight cone 5 was well dov.Ti and the cones in the saggers indicated that the cone ^ heat treatment extended to all narts of the kiln. (h) Fitting of glaze, slip and body. The results of the Bloomingdale Stoneware nieces showed that the method of dinning was probably at fault, as the glazes and slips rolled and beaded considerably. (c) Biscuited tile trials. The glazes all developed well on the biscuited tile and the tabulated results as to color were obtained from these trials. iriiMiiy _ v. i'-n ;j: ' W"' , f S;' '-^‘> -V , '.* -fV ■■’'>''V-' T ■'’"■/'• 'I tef '‘'v'^ * .’«•'• 4 • ^ . 1 *•%• «^ ‘ * jvi . ' '4,1 >^H4a r ^, ■•’^T®Kl|L^^^ J fete: ‘ ^ '^vt: m- 'm*- ^ ■'..1 'd'Y V-' ( • ‘'‘ .'‘/r''* T .ybfcj^BwPhaL'-l ‘ ■ *J.3» ■ StoCT ' '*1 Y- . c-~ " ■ ■ - ='«:« '"■a *'*'.*-' ■■ ,T„ fr'' liB' “ ■ ' ■ :" .- V ;.-:^.^i’;p:^ispwi: '•/■ * H ■«'■<. r^; . ., . ■ . S^f, '■ -'■ •■'.'W* .''.f j ■' vy;'',.:\*t'- I'J.J I iAJ* ' '*.HSb.|, ». ' '.V VjdMfflfiffi® . - V’ 4 V!^?v V. ' ^* ’ J .,•■-*■•! A'T’Tv -‘- ••* T 'A. --^owifaB c ■ ^ u '". < ' '• u ' * 1 ^ IT: r ' ' -1 II fcv*A‘ . '" -.I’M 14 T bJoI e ITo . 1 Equivalents of Coloring Oxide employed Color Oxide .005 .01 .02 .04 .07 .10 1 U 2 O 3 Trace F51i ght Fai r Good yellow I.'luddy Brown Almost B1 ack 2 TiO^ Fone Fone Fone Fone Fone Fone 3 2Ka^3b03*7K^0 Fone Fone Fone Fone Trace SI i ght 4 C Fone Fone Fone Fone Trace SI i ght PT *FeC (Ba) Trace Sli gbt SI i ^-t Fair Light Browni sh Almo si muddy : Muddy 6 ItFeO (Mg) n H II II It 7 2FaSbO. . 7KnO 3 ^ Fone Fone Fone Fone Fone Fone 8 U 2 O 3 T race Sli^d^t Fai r Good Yellov.’ Mu ddy Almost B1 ack 9 T 102 Fone Fone Fone Trace Tr ace SI i ght Brown Yel- low 10 Fe 2 O 3 Trace Trace Sli ^t Pale BroTO Pale Brown Pale Gray- ish yellow 11 Ce 02 Fone Fone Fone Trace Cre am Crea.m * FeO in the original Bristol glaee, with. 1 equivalent harium. oxide. FeO in the original Bristol glaze, except that .1 equivalent magnesium oxide replaces the barium oxide. Fos. 1-6 inclusive Bristol Glaze. Fob. 7 ^ 11 inclusive Fritted Glaze. / 15 VII Conclusi ons. 1. From the results of the Blocmingdale Stoneware trials there is obviously something v;rong mth the applications of the glaze and slip on the body. The writer has had similar experiences 7/ith attemnts to dip Bristol glazes on this same body which v/ere corrected by snraying the gla^ie on. A better application could no doubt have been made by spraying. 2. The glazes on the tile trials were well matured, showing that the glazes are suitable for maturity at this temnerature. 3. Of the two glazes the Bristol appears to have an advantage over the fritted glaze for apnli cation to the green nieces, as they, in general adhiered better on the green nieces than the fritted glazes. 4. Coloring Oxides. Of the coloring oxides employed, only uranium and iron oxides annear to be worth while as a commercially practicable coloring constituent. The higher members of the Uranium* series show up gray which is, no doubt, due to the excessive amounts used. Iron develons a fair ye]low, but one that is rather indistinct and slightly muddy. i6 Part Tv;o I Change? in Glaze Co^n-nosi ti on. It appears that the Bristol glaze "behaves "better than the fritted glaze on green "bodies as the Bristol glaze was adopted as the standard. The R. 0. mem"bers of the glaze were varied some-vdiat to determine what effect, if any, this would have on the color oxides. The two variations are as follows: "X” Bristol .333 .334- CaO 0.55 Al^ 0^ 3.3 Sio^ .333 YnO "Y" Bristol .350 K2O .317 CaO O. 55 AI 2 O 2 3.3Si02 .333 YnO The oxides were used to replace equiva,lent amounts of calcium oxide, as in Part One. Tv;o other oxides v/ere employed in this hum, which were not available for use in the first hum, namely tungstic acid, and molyhdic oxide. These were used hoth alone and in the presence of .05 equivalents of manganese dioxide. 17 II Pren arati on, Blending, Aopli c ati on, Firing. 1. The nrenaration of the glazes was the saire as outlined under Part One. 2. Blending has already "been outlined in Part One, the same method being emnloyed in this burn. 3 . Application. The method of an-^li cation was different from that employed in Part one. Instead of dipping, both the slip and the glaze were ap-tlied by spraying, which gave a good even coat, without showing any drying cracks. 4. Firing. The firing schedule was the same as that emnloyed in the first burn, the si ^^t cones and the Seger cones being the same and the burn going to the same cone--Cone The writer could observe no indications of reducing conditions in the kiln. Care was exercised to avoid forcing the fires. The cones indicated a good even cone 5 heat all over the kiln with the excention of two saggars in the bottom, v;hen it v/as estimated the heat was cones three and four re s' 0 '= c tively. 18 ill. ixesults. 1. Application. The application of the glaze on the green body was rather thin, but it was thick enough to indicate that the body, slip and glaze were well fitted at this cone(Seger cone 5). The majority of the glazes indicatea that they would mature at this cone, as is shown in Table No. 2. 2. Comparison of the slips. Of the two slips, the vitreous slip lends itself most readily to the proper maturing of body, slip and glaze at cone 5. 3. Jiiffect of absence of iiarium on the iron oxide yellows. A decided difference in the tone of the iron oxide yellows is shown in the absence of barium oxide from the HO members of the glaze, the ones without barium present being much more clear and uniform and avoiding the muddy appearance altogether. ■ ■ T:. ^ t''* ; '.Nri b . . .V^-OC. . >, u j. j : . .’ '; f . ■ ■ '• . V'!: «Iivi J4 ■J.i'. •.•O’t Ji;nr;M-'C3 5i: / “‘'■/ c).‘ \ :■,<■) «7is'., i ''i j ‘ ' . L ' v; \ r. r- *.^ } '">m0;> ■' ,w 1." \l ■ ■ ^ ■ , ’ :• o ' >, .' .'< '■ Olfi .'.oV '.'0 o ■ '^y .ru: hri r -1 4^ . ' - ■; • ?. ixy''!.' eh IrC ■.?: i. a ' ' ■ i' •o - : • 0 .'.: ■ • .■.’i •< ,s t-r. ^ • : i r» I ., ;0. j J'l'O'i L • t '.'Ol ■ ■“ .. i'. Ji:v ri i.xj -■il- 'Ij I J r. ^ *■ . ^X: V . . ; ,;c‘.-- i;r SVO*i( I ..<-. S tail: .0 , - I, 1. tj{.. - V *-;'■''' . J‘t\ I ’v . o r " , • w , r ,. • 4\. - ’ T ... , .Ov-. ...... \ r- . ..bCltOl .% ,'>.; 19 Table ilo.E, iJata on the tiaturity of the Glazes • Amount of oxide used .005 .01 .02 .04 ,07 .10 Bristol: ^2^3 0 X X X 0 0 ij'egOg X 0 X X X X X X X X X X MOOg X X X X X X ”Y” Bristol: °8°3 X X 0 0 X 0 X X 0 0 0 0 X X X X X X UoO, 0 0 0 0 X 0 Original Bristol LIoO_ o • X X X X X X HgV/0^ 0 0 0 X X 0 •' & MnOg X X X X X X MoOg&MnOg X X X X X X UaiOgjg & Feldspar ji^ritt 0 0 X X 0 0 0- indie a,tes glazes not matured • X- indie extes glazes which matured. A* , ' 1 *' ’ *by f"' ■ ^ vji . toii^ .i''. i {) X 0 ' ' ,/■ . 1. . jiL « • « j _ ■'* ,. , •■> ■' ^ ,r X - X . ,'\ >v ■ ' \ ,r ' \,t-' ■■ V ,v ' . vW' V ip ■ .1 •\ ■ V ' fe-v , '"O ■ , -^j’. .': ' S )£ . . ' ' ' "' '1 • ^ ; “'• r^; 5X/^’,;.' '•c ;■" s 1 ’ ' >;;X' ■ ■r' -‘ V *- '.'■■■ ■ ’v :: ( *• . V'''--‘' ■ s t ■ <■'•?' X , .;■> X ’ C- . / '■ V ' o; T \ -' v'. ■*-'•'* S' At^* ^Xl Coloring Oxide .005 20 Table No. S Colors Obtained 01 eg. .02 eg. .04 eg. . 07 eg. .lOeg. ’’X” Bristol Trace Slight Pale Muddy Cray Almost Black FegOg Trace Trace Slight Pair good good yellow H2WO4 Hone None None None buff tilt- slightly buff ed None None N0O3 None None None None None None nyit Bristol Trace Slight Pale Muddy Cray Almost Black Fe 0 Trace Trace Slight Pair Good buf good yellow H2WO4 None None None None tinted yellov; None slightly buff None LloOg None None None None None None Original Bristol Mo Og None None None Trace Slight Slight pale brovm H2WO4 None None None None pale brown None None H2WO4& Light Light Light Light Light Light brown LtoO£ brown brown brown brown brown MoOc2 8a light light Light Light Light Light brown MnOg brown brown brown brown brown U(U0s)3 Slight Slight light Pair Cood Blackish V . 1 ;> ST" n ' . ^ ✓ or 1 71 j fiA« , • o 22 XV. Nummary. 1. Uranium oxide develops good shades of lemon yellow, except where too much is used, where it turns black. 8. Iron oxide develops good colors of yellow-buff. The iron yellows are, however, slightly muddy in the presence of barium. 3, Tungstic oxide and molybdic oxide of themselves develop no color With .05 equivalents of manganese dioxide they develop light buff browns. The manganese, of course, predominates in producing this color. 4. Ceric oxide produces only very faint yellows, which are, of course, impracticql for use in terra cotta glazes. 6. Titanic oxide, also, develops only faint colors, which are useless. 6. Leukonin as used develops no color. 7. The application of the glaze and slip by spraying leads to the best results as to the fitting of the body, glaze and slip. 23 V. Conclusions, The Uranium oxide color is the best true yellow of those used here, Uranyl nitrate fritted with feldspar gives a good clear lemon yellow, which is very promising in appearance. The and ”Y” Bristol glazes show no improvement over the original Bristol except in the ease of iron, which has already been noted. The one which, in my opinion, is best for use is the ”X" Bristol, because of its conformity to the typical iiristol HO formula and because it develops a fine gloss and allows of con- siderable variation to allow for fitting it to any body on which it is used, iron oxide colors are very good, especially v/here a yellow with a slightly buff tinge is desired. The advantage of iron oxide is its cheapness and availibility and comparative purity with which it can be obtained. The tungstic and molybdic oxide glazes with manganese are not true yellows at all. Their use as such is therefore impossible.