PRODUCTION OF GREEN SURFACE COLORS ON RED-BURNING SHALES By EARL BOGGESS BAKER THESIS FOR THE DEGREE OF BACHELOR OF SCIENCE IN CERAMIC ENGINEERING COLLEGE OF ENGINEERING UNIVERSITY OF ILLINOIS \ V • ,T/. Ij 476973 It ■■i.rro^ ' iic Digitized by the Internet Archive in 2016 https://archive.org/details/productionofgreeOObake TARLF. OF COFTEFTS P n p- c I IITTROPUCTIOF 1 II EXFERIICENTAL PROCEPITPE 3 1. General plan 3 2. Materials used 5 III E10PERIL31TTS AllP RESULTS 6 IV SCOPE or nrvES^IGATIOIT 9 V SUIU’T/JIY OF results 9 VI GEITEK.AL COUCIUSICFS 10 VII BIELIOGPAPKY 11 i \ , ?r i J W fcii.K i "'l‘' ’.'V I INTRODUCTION The demand for new and novel color and texture effects on face brick has induced a great development in mechanical devices and in firing treatments for the production of such effects. Green colors are much desired by many producers who recognize their possibilities in the market. These colors must generally be com- bined v/ith surface textures mechanically produced. Grazed brick v;ill scarcely fulfill the requirements owing to difficulties in manufacture and in firing, such ware and the expense of producing it . In som.e instances green sha.des appear on normally red- burning clays in certain portions of a kiln but the production in quantity has not been attained by more thon a few manufacturers. Obtaining of such colors apparently depends upon the firing treat- ment as well as the composition of the clay. Limited information is available from ceramic literature on green color production, other than in glazes. In these, the coloring agent ma,y be copper, chromium or a ccjmbinat i on of uranium and cobalt. In some cases iron may give a green coloration. This may be especially noted in glasses containing iron as an im- purity. Calcium, barium or magnesium probably aids, but iron unquestionably functions as a coloring agent in the case of green surface effects on clays. Seger ^ f requ ently refers to calcium as an aid in the form- ation of greens. He states, ” Sy the reducing action of fire gases an iron bearing clay beccrnes an intense uniforir. black due to uhe «■ . ■ ' ■ / '’1' ■- h.<"l ■ " ' >,'. 1 ^ »•»»* .i«-;, ^7-i> * ' ■' • W%f' r>- :- \‘ ' ■ '¥ -W' ■ '* . •-'••• ir/ '>« 3' - . ,t -‘ ■ . ’'''ti 'i- ■•'l tf^Elw [j[Cjt > 'i V' ■'-■ --MI-™* I ^ t, A iji/ri/ .n ‘ 7^ _ -7*> y ‘ '•^. '^ P'S 'PaK^^^ I ;fc.4''l«»W ;i(,' i.(j Viiu««* • i i|^ w ti'' _L. ' ■ . ■ ;|i'. •- " -^' '• ^>":>; ■;.* :-'‘f ■ •■•-■ •; tl ^ ,• -. V ■. ■ ■*' ' ■ ?:,»:^'!>’l. -; sji^ » ! J ' rr!.. " .ij »« .iiLia W W y .vT, fonnation of f erroso-f er lic oxide, ferrous oxide and metallic rion. By a previous reduction, an oxidizing atmosphere produces sha.des of a lighter color, passing into white or light green". He further states that in either oxidizing or reducing atmospheres sulphur is ahsorhed hy calcium and iron in cal care ous|cl ays and gives a dense red color at moderate red heat. The red is completely destroyed at a high temperature and is changed to the normal greenish yellow color by the action of reducing gases. Lime produces a neutralizing effect on iron colorations. A yellow burning calcareous clay, when the chemically combined water has been expelled, becomes red and still further heating changes it through white into yellov; and orange until finally on vitrifica- R * tion the color becomes green. In a strongly reducing atmosphere, a glaze containing 2 % of iron oxide and 10 % calcium gives a greenish blue similar to the color of Chinese Celadon or " sea green". Such greens are complete- 4 ly destroyed in an atmosphere containing 20^^ of carbon monoxide. I’roin the literature, a most logical treatment for the production of green surface colors or normally red-burning shales would seem to be the addition of varying percentages of lime, magnesium or possibly barium and firing and reducing conditions. under varying oxidizing J ' . . -3- II EXP]!UlIT,tENT./\L PROCEDURE 1. General plan .- The general plan of procedure in the experiments consisted in firing prepared trial pieces to tempera- tures ranging from 950® to 1150®C, and under varying atmospheric conditions. These treatments produced "bodies varying from a porous structure to those of a complete vitrification. The atmospheric conditions were varied from slight reductions followed "by either long or short oxidizing periods to that of heavy reduction followed by either short or long oxidizing periods for the respective heat treatments. Similar reduction and oxidation treatments were repeated v/ith a period of neutral atmosphere follov;ing each reduction. The experiments were carried out partly in a coal fired test kiln and partly in an electrically heated combustion furnace. In the coal fired kiln reducing and oxidizing conditions were maintained in the usual manner by damper and fire control. Atmos- pheric conditions in the electric combustion furnace v;ere regulated by use of city gas or carbon monoxide for reduction and carbon dioxide for neutral and air for o-idizing conditions. The electric furnace and supplementary apparatus is shown in Eig . ITo. 1. Carbon dixoide was produced by means of the Kipp generator c attaining chips of marble and dilute hydrochloric acid. Carbon monoxide was produced by passing the carbon dioxide over charcoal heated in an electric combustion furnace. Eor an approximate control of gas mixtures entering the furnace, all gases v/ere bubbled through water. An Orsat apparatus v;as used for * 5 , .rr# jr. ^ "A fPPP^^f^P^ ''•• 3 S‘^|' '; ■ Jl^^i *f p- *y -.•■;. . ^'- . fr '^;ia ' 'i ufi, r.' • ■-' ■ ‘ W'> J' ' ‘■'Y ;, - ’ ’ i ■ I ’ ^OillBW'ijI |»‘« P r ISV'iv ■' /*:c X ' y p4 • . ■•'Sh' r i| i, .-y/it I . ^ f., M,j» ' . 1 - ^1 ij , wi . ,; v-H V. 'PSTJ \'^ _‘ TA-'xUr*r\ •: ! ’1 . .-y ;v ii r ,1,*' ■ * . ..- y* :■ k, i I . J • *'• ‘ 1 - ' i Tw *'» A.. ■"V' ‘‘ ff-'A n* ' >■ ''X:- . ’?Sii ’ i • ' . »’*'^ll. ' • '^*‘ ■ ' V ' h , tr^,, '.v.t V ii^'. .' . •„ ’-V . 'i' i- Fi' 'rjj(v >'■' ■ 4‘ .*'“ ' ‘,?- >Vi , r ;v|-.K,v M %f# ' •^'V f" 4 & iv » ■ y^.;r .;i> i,; (.* • by. ri !. i' ' Av '•'>f ■ .i.f'^i:-/ 0" 1$ »■,; , > , ...vv d ,>v f ’•» ;. ' .yi'\ • ■ (: ■: . iH • ' • •■,'■ ■.’ . • . !■ ■>' - r- ; * |^Tt.. ;o-^,.;i;-' r ;' ;,51 f * f' .. _ «^is .' ■V'' 1 '"I ^ ' '1 '<■■■ 'ttii^- yh^‘ ^ '*'“’ ■' ".'■ ■ • • V. ' ' 4 '’ • '^: - 1 « ’ 4 ,:^ I "“ r'*v XfjSfi^ir '^;^^'•'•f)l^!^^'ic^^i|f■ isi-rViSW?! , ■ > . . ■ '‘'■■■■r'^ , ■ ^:/, v'!l ' #2 -i >.,^ i>j. ,j;’^ ; /v^;’ , 1.55^,^^^)^ • ’!-Vw‘:v .’i . ; . -, ' ? .tu..-^.'*”^J.->i?'.,' ' ■>*.•' ■ .A '"IV ^ ^ •'-v'- I, 1' _.itL; W'-.:‘! .r. 1 "*^' '‘Ijfi''*" " i'll*^TB|liM|fltW i'll i I i I .•;'"Sf4*i -7 - Mixture Ko.21, consisting of 96% Galesburg shale and 4 % of ^aCO , was subjected to varj^ing heat treatments giving a body 3 ranging from _orous to completely vitrified. For the different heat treatments, the atmospheric conditions in the furnace were varied fran strong reduction by means of city ga,s , followed by long oxidation periods to light reductions followed "by short oxidation periods. Such treatments resulted in color effects similar to those produced in the coal kiln. -Below vitrification, the pieces were of a light red color but upon becoming vitrified the reduction resulted in permanent colors varying from dork brovm to black, the colors becoming darker with more intense reduction. 'i’he dark coloration was chiefly due to a reduction in the iron in the clay to ferrous or metallic iron and the density of the vitrified body prevented a re- oxidation. From these results it was again evident that a permanent green color could not be produced on a non- vitreous body. It was next thought advisable to follow each reduction by a period in a neutral atmosphere before introducing oxidizing con- ditions. To obtain the neutral atmosphere, carbon dioxide from a hipp generator v;as passed through the furnace. -^'rom the assumption that a green coloration is a result of the formation of an iron- lime-silicate, it v/as hoped that a period under neutral atmospheric conditions would give additional time for such a chemica.1 reaction to become more complete before introducing an oxidizing atmosphere. The use of a neutral atmosphere gave the same results as y/ere obtained v/hen the reduction was followed immedia,tely by the oxidation period. '•*'i ' ■•; i.' ■ ■ ' ' • • . -s?i’>.''T 'fiwl ( “ k. * ■ .'. i • . I ' •.'»• ■•■:'. ' ' ' -.- l-t ' , '.J ' .”i.«'-**^”i kJ*» ■ v*n i ‘? ■/.- aj)'. .A-*.r <4 •|51 ") ;«)' it ', *i''^ ''.<• V a / . ' */ ' ^. ’’ .. Lt.' -* 9 £. • •* -Sv. _, ''" ' J V II V lr\ Ai ' , V ; •■ *; v^.: if i: n u x # ’’’ ^ A ^^v"' 'x ''^ tT '"^-t'tw-. t»\' \iVVs(f. i / •‘''‘^i 1 ^ )pi 1 • • ... A 4 * '• ,-/ • ' ' i 'I'jf^ * * _iy ^‘'- • ■ ^. *' •■’j _ . ..'Xxl • ■'' ’ .-^■ 3 *'i ' • 4 MH. “* ' . ;><■ r. '* t; .' - ! . t.--'/; '.r* i.j .r.r'.^ViJ ■, ■■■■■.•/, ^ <.?Ui M I ' * ,’^ J . ■• V ■ ’.■ •'■(, - V ■ •■ ••iwj i- L*-1 •'■*■■' ■•■ • , . » ■;. „ i ■■'tJ’‘' .»{•., • < • r .', > 'J '°^ ' *.n ' f, ' 4 ? i' 4 't f: ■"'■^ «.* .*J, ^ v>* V, ^■■sm .4--- ri'fgf-’-.fvn.' 2>fc(?x4- ’*l- !.' i'tf* '4 .; • ■|tf.^c»' •* -5 ' -'* .• ., , >■ . / v^ T.,.’ • 'r- ,. . . ’. -A '-ai. xttT:^... „ ■ • V. mJ^-M '.•., . ^';i^:'{;' A? K 'yti' .£.;.„ «,t;^ - V;^ siifH'' , "^’j0Sr -3- The next treatment consisted of vitrifyin.:- the trial and then subjecting it to several moderate reduction periods, each followed by a cooling of the piece in an oxidizing atmosphere. The latter was accomplished by withdrav/ing the trial fron the fur- nace for a short time after which it was again placed in the furnace and given a similcr treatment. ''.Vith two such treatments a distinct bluish green color was obtained which did not change with repetition of the treatment. A small piece of mixture No. 21 \ was dipped in water previously saturated with calcium sulfate. After drying the piece was placed in the furnace and heated to vitrification. Upon vitrifying the trial overburned and sv/elled thus eliminating it frotn practical conside rati on . Calcium sulfate will deccmpose to a greater or less extent v/hen hea.ted in the presence of iron and silica. 5’rom this fact it v/as thought possible to decompose the sulfate thus leaving the calciujn in the body to combine with the iron and silica.. This result might have been obtained by^ further testing but it v/ould be of no practical value since portions of kilns are often overfired and this v/ould produce a tilting of the vrare. Reducing conditions were finally produced by passing carbon dioxide over hot charcoal in a combustion furnace. By varying the temperature fran 650®C to 700°C, the carbon monoxide content of the gas varied from 8 to 20 %• Mixture No. 21 was given reduction treatments with gases containing 8% and a.gain v/ith gases containing 20^ carbon monoxide. Both resulted in a dark blue coloration. Further investigation «•' ' ■7''y 's” ' _ . V.. ' ,■.'*■•' *A'-,V'.'*^; '5/,* . . V :, ..i'fev i.^ -f' ^ ^ -'y (■•' - ■ iw^;if ' . tv' ’Vi«-^^i®' JS|l'. *■'"•■ ^'t‘ *ii* 'v K"- '«-■■■• ••■»'■■; Vl*'!: .« \ ••'- ■_ St'/SH ’ »’ -wife ' ' ^ , , : j-\. ■•: '^ ' ■■■ ' tv •' • •■* '■ ■• - .' ‘ V' :«T, «« ' • ‘ • ■;}'. ■; if.**, Ef'> ’ ■ * : f^*‘- f y «. ‘T:»V 4 : #>j ' *,, '; *r. - 4fkj f ^ ‘f ' ' lit0t :s^ ’■ ?'§&;p V? . : ‘ I E.‘,:c r -43^' - '•’ v' <3)^; ,_ ’■ ^ '•.I' ^ I y 4'* *,«■■■ V’W. ;(■••’’. 7 ‘ '.• 5V3t“i(,'i(i-^ '"'■ ■' " '■ '' ' ' '*' ' 't-" ■' ''^ 'A S vis, * ]^ ' 7 • / : w, 'iJ::>"^ .•.7, /■»' IV ...n r ii ^ J|)'. w v i ^ J ' . ' — ,, . , , . _, , , I'-V''’ r"* ‘ *f' •'^ *'i‘~WiilHh’''’ ~^'' '''if'' " '' ' ' •' ‘*^*■1/*^ -' I. 'vV. -9- mi£;ht have given more satisfactory results v/ith the use of carbon monoxide as the reducing agent. Mixture No. 25, consisting of North Carolina kaolin 55 silica dixoide 35, ferric iron 3.5, calcium oxide 10, potassium oxide 5, and magnesium oxide 1.5, was vitrified and reduced by means of city gas. By a single cooling in the air a good green color was ootained. The chief difficulty was due to a very short vitrifica- tion range which resulted in giving the piece a marked glaze effect. This v;as undoubtedly a result of the fluxing action produced by the chr-mge of ferric to ferrous iron and the high lime content. Trials drawn belov; the vitrification point v/ere of a. reddish brov.Ti color. IV SCOPE OP lilVESTIGATION The scope of this investigation was limited practically to a study of the temperature and atmospheric conditions favoring the development of a green surface coating. A study of the body compositions v/as iripossible until a. proper firing treatment was a obtained after which only^linited amount of tiine remained for further inves tigati on . V SmMARY OP RESULTS The results of the above invest igati ons may be siAirmar- ized as follov;s. r T ' V ,^^V ^Tf^XT / -.,• • r-. ...^ - -.f ^ ' •■v'l’^l'.'^. i '"•' ‘'tI ;. T iffl" "l| ■fc '1^ hy^‘ 'iTT ii B i r T t^i t T i lirW ^ ■'• ^ -■'■ -m, igf.,- ■ ' J* '.■;5-'Si •■Wfj/’- ^ 'i '*.• -;iI'-'‘' ■';'"■ '“•■O'"’ ■*^’' — '' Vvt.’ . 'l' • 1. <■ *'"i 'I ■ ‘1. ' ' Kt V .1- pv( S* ’■■ ’ ■'. •' " ,-' I'i ■ "tf: ^g^/^.»-;.rA--y. • . w^-'.'.; ' ■/ ;' '■ _^ • W> ^f^fJ"’Wit *lf^' '' 1 • ■-'■■ ■' '•'v^^'*^ ' •• ‘.‘’M V* ^ , Hi '^ 5 !^ >• Is fei', fiV w yi :J'\ . V. ■.•'■•• ■ V.- ■'%&•■•'' ifi ji ^ ..-■•»■ •- W. — . ?3 *♦ jr . ' ^ i **y . '.M^-* » . ^>.»-. . ' J ■ * . X ■• ■ - Ti|pf^ .m^ .. ' ?• ., ^ ; 'v.T«gr ^ •, '., 'V . MW- '^ ' ^ " r ^ ^ '’ •■- - 7'‘ i ’ "i^ ■ / , '^T -y,^' A ,- ''■ ^ '- T-P-'-;.'-' ■ ' wM-V'«nj .. „i I « 4 ,• ■ ■ ■ *' t. i>v'' ■*- “•s^’ r-jf •‘■*.^5v '? ’^.. . ^ . , , . . rp,, ^ ;, I <. ■BlflBjii' 'f ;.v, fr,.^* i- .1. % ■m A" \i r^iwd - / vik - 10 - 1 .ColorstioriR produced on a. porous ferruginous cla.y "body liy means of reducing conditions in firing were not permanent. 2. Wlien vitrified, a ferruginous cl-y v;ill retain sur- face colors imparted to it "by reducing action of kiln gases. 3. A red.ucti. on "^eriod fallowed "by an oxidation period at the same temperature did. not give a green surface color. 4. A reduction period followed by an oxidation period accompanied by a cooling of the cloy is favorable for the production of a green surface color. 5. The presence of lime in ferruginous shale is favorable for the production of green surface colors when given the proper firing treatment. 6. A neutral jjeriod following each reduction is un- to aid in better surface colors. V I GMIEH AI. C '"FGT ng t OITG Fr cm the ab o ve r e su Its, the following conclusions ma.y be drawn: 1. A red-burning shale containing 4 to 6 % of ca.lcium carbonate will give a green surface color if fired under favorable conditi ons . 2. 5'avorable atmospheric conditions for the production of green surface colors consist of moderate reductions followed by strong oxidizing periods accompanied by cooling. 3. The heat treatment of any "ware for tine production of 0. surface color must be sufficient to produce complete ■vi^ro.j.i- ca t i on . ] f • i, Jv’ *1 / - 11 - 4. The £;rcen coloration ic prohahly due to the fonnation of an iron-lime-silicate. VII BIBLIOGRAPHY 1. The Hole playet? hy iron in the burning of clays - Professor i^^dward Orton. Trans. Amer.Ceraia. Soc. Vcl.5, p. 377 2. The compositjon of Chinese Celadon pottery. - Jour. Amer. Cerain. Soc. Vol. 2 - p. 55. 5. Influence of oxidising and reducing geses on the color imparted, to porcelain by coba.lt and iron. Professor E. Bemiour. Jour. Soc. of Chemical Industry’. Vol.15, p. 533 4. Porcelain, influence of the a,tmosphere of the kiln on colors. Professor E-Bemour. Jour. Soc. of Chemical Industry. Vol. 17, p. S45. 5. Calcium carbona.te in clay and its influence on the properties of the latter, y^-ith special regard to the manufacture cf front brick. Seger, Vol. 1 - p. 336. 6. The comiposition of Augite. Professor Edv/ard S.Bana. A System of Mineralogy - p. 481. 7. Mote on brick colors. Professor -German A.Seger - The Collection of Writings of Herman A.Seger. Vol.l, p. 106.