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Scholars' Mine

Bachelors Theses Student Theses and Dissertations

1933

Aventurine glazes

Felix Fraulini

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Part of the Ceramic Materials Commons Department: Materials Science and Engineering

Recommended Citation Fraulini, Felix, "Aventurine glazes" (1933). Bachelors Theses. 309. https://scholarsmine.mst.edu/bachelors_theses/309

This Thesis - Open Access is brought to you for free and open access by Scholars' Mine. It has been accepted for inclusion in Bachelors Theses by an authorized administrator of Scholars' Mine. This work is protected by U. S. Copyright Law. Unauthorized use including reproduction for redistribution requires the permission of the copyright holder. For more information, please contact [email protected]. " , AVENTURlNE GLAZES

BY

FELIX FRAULINI

.A THESIS submitted to the faculty of the

SCHOOL OF Mll~ES .Al\ID METALLURGY OFTfIE UNIVERSITY OF MISSOURI

in partial fulfillment of the work required for tl1e Degree of

BACH:ELOR OF SCIElfCE IN CERAlVIIC D-GIl'fEERING

Rolla, Mo.

May ~, 1933.

Approved by ••••••••••••••••••••••••• I~~TRODUGTIO~ ------~------1-2

SU"PE OF INVB1STIGaTIulJ - .... --.------3

1£IETI D ~ INWSTIGAtfIUN -~------~-----3_4

rSE~ ------4 1ImTHOD F PREPARING GLAZES ------6-8 APPLICA ION OF GLAZE ------9 FI ~G --~------9-~O DI~CUS IO~ OF ESULTS ------11-14.

EFFEC" F C01TTROLLED COOLI1~J- R \.TE ------15-17 DISCUSSION OF RESULTS ------1B-19

C "'C USIONS ------20-21 IillCOlwl\lLilll- ATI l~ ------22 .AP LI ~ TIOli 'ro TtT IIJDUSTRY ------~--- 23

AGGJO~~iJGl\iIENT ------24 BIBLIOGRAPHY w______25

ABSTRACTS -~------26-28. (1 )

AVE.NTURIl\fE GLAZES.

IlfTRODUCTI'Ol\I •

The production of an aventurine efface consists in the addition of an exce sa of a metallic oxide 'to an allc- aline glaze. The glazes are mostly fritted and in the glost fire the glaze liquifiea and dissolves more or leas of the metallic oxide or oxides present.

It/is the concensus of most writers that at the maturing temperature it is a supersaturated solution. In cooling the capacity of the glazzy liquid to hold the dissolved oxide in solution is lessened, and the excess is precipated as thin plate like crystals or spangles.

Crystalline segregations are not new in colcired glazes. Aventurine effects are found on Japanese vases made centuries ago. 1

Dr. Maeckler, by request of Director Dr. Heinecke. of the Royal factory at Berlin made the first scient- ific investigation of the phenomenon, which was pUb-

~ lished in 1896 • .L

In a ~ublication by G. Vogt, technical manager of the National factory at Sevres, says that the first crystallized glazes were made at Sevres in 1884.1 J Koerl1er2 noticed that Uranium Oxide cOlubil'led

\rvi ttl lead had a great i11clination to fornl an aventuriXle

like glass. He found this also to be true witll Bismutr.l..

Riddle3 made a good aventurine by supersaturating

the following frit with some coloring oxide, ferric oxide working especially well, giving a rich red color. Following is the empirical formula and batch

wei~~t for Riddle-s glaze.

0.25 fu:,O 4f",J

0.25 Na20 2.25 8i02 0.50 CaO :Batch weight. Potassium Nitrate 13.95 parts. Calcium Carbonate 13.81 ·parts.

Flint 3?29 parts.

Borax -----~------26.38 parts Flaky boric acid -­ 8.53 parts

Petrik4 found that by melting dehydrated iron vit- riol and common salt together, flakes of iron oxide are produced which dissolve only with great difficulty in a molten mass and give accordingly an aventurine effect. SCOPE OF Il\}VESTIGATION

The object of this study was to nQtice the effect produced upon the crystalline growth in the glaze by the variation of E203, Fe203' and 8102, ~,d to notice the effe"ct of cooling upon the crystalline gro,vth in the glaze.

lmTHOD OF nrVESTIGATION

TIle following glazes were selected for the end members of a 20 member rectangular system. The graph shows the position of each of the 20 members in each series.

4 0.75

o•80 ~~---~--~.....-l"""------t8

16 (4)

The compo.-sit ion in terms of equivalents of the

corner members for both series; "Att (5.0 equivalents

It 8109 ) and series Bn ( 6 • 0 equivalents 8i0 ) is pres- j.;.,J 2 ented in table I

Table I Series A.

Corner l~o • 1 4 17 20

Na20 1.0 1.0 . 1.0 1.0 0.95 0.95 Fe203 0.75 0.75 AJ.203 0.10 0.10 O.~O 0.10 B 0 1.25 2.00 1.25 2.00 2 3

SiO2 5.00 5.00 5.00 5.00

SerieA E

Corner No. 1 4 17 20

Na20 1.0 1.0 1.0 1.0

Fe203 0.75 0.75 0.95 0.96 0.10 0.10 0.10 0.10 A12 03 B2 0 3 1.25 2.00 1.25 2.00

Si02 6 •. 00 6.00 6.00 6.00 (5)

luIATERIALS USED

The materials used were flint, No.4 Eentucky ball clay, borax, iron oxide (red), ~,d soda ash (Na2C03). METrlOD OF PREPARII~G GL.A.ZE.

:.Frits were prepared for corners l1umber 1, 4, 17, and 20. For each of these members, all the ingredients were fritted except 0.10 equivalents Al203 [md .20 equivalents SiOZ' which were later added as ball clay to help suspend the frit. The composition of the raw frit batches are given in table II Table II Batch weights of the corner members.

Series. A.

Member Borax Na2C03 Ferric Oxide Flint

~ 238.5 39.75 J.~9.6 288.0

4 381.4 119.6 288.0

17 238.5 39.75 151.'71 288.0 20 381.4 151.71 288.0 Series E Member Borax N~C03 Ferric Oxide Flint

1 238.5 39.75 119.6 348.0 4 381.4 119.6 348.0 17 238.5 39.'75 151.7 348.0

20 381.4 151.7 348.0 25.8 parts of ball clay was added to each frit for the 0.10 equivalents of Al203 and .20 equivalents

SiO? i'-.I The four corners were fritted, the drip method of rritting being used. The frit was dried and then ground in a porcelain lined pebble mill until the frit passed through a 150 mesh screen.

0.10 equivalents of Al203J in the form of ball clay, was added to the frit, and the frit again ground, with water, in a porcelain lined pebble mill until the glaze passed through a 150 mesh screen.

The specific gravity of tlle glaze waS adjusted to 1.48, and the intermediate members of the rectang- ular system were made by volmue blending of the C07- ners. Tab1e III (on next page) presents the percentages used for blending of the intermediate members. Table III.

Member Corner No. 1 4 17 20

1. 100.0%

2. 66.67 33.33%

3. 33.33 66.67

4. 100.00

5. 75.00 25.00%

6. 50.00 25.00 16.67 8. 33~~

7. 25.0.0 50.00 8.33 16.67

8. 75.00 25.00

9. 50.00 50.00

J.O. 33.33 16.67 33.33 16.67

11. 16.67 33.33 16.67 33.33

12. 50.00 50.00

13. 25.00 75.00

14. 16.67 8.33 50.00 25.00

15. 8·.33 16.67 25.00 50.00

1.6. 25.00 75.00 17. 100.00

18. 66.67 33.33

J.9. 33.33 66.67

20. 100.00 APPLICATION OF GLAZE

The frit settled out so fast that it was impos­ sible to dip or spray the glaze on the trials; there­ fore the glaze was applied with a small camel hair brush.

Firing

.The trials were fired in two saggers in a muffle kiln to cone 3. The kiln was fired at the rate of 1100

Centigrade per hour to cone 1, WI'lich was reached at ".~

1080° Centigrade, and cone 2 and 3 were soaked down as this temperature was maintained for 1t hours. (10)

~ I

L... r-+·+---I-t~I·~';-:-..j..-+--.. I:~+-- f-.f--;-Il ~-+~-I--H"-i~-~-!-:-+-·I--1I-1~-I-+~'\.,,,·I-'--+--+-!~-~-~-·~.. -.:.-1. I-Jf--i--. ·-t·-:-·~_-_·'--l·_·' f ,--!- -. ·-I--+-f-<~·,·~'-·+-~·-I-·-+~"~~-~-l-:.··I~~-I---h~-II-I- X ... - ~ -~:_+-i._.! ---j!-l-4-I-II.-!--4-:C-1-e \l -'l--~-1--f-I-t-'-",-..,l:-I- _.- - .-- --- :- .I·_t --\-'1' -~·-.,o:-I~-f--'~'"-'1.-4..-.--

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_!--_~- "

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-~ -1 j- , .... "--+-..l-I--f..+-f-lf-+~-+-t-+-l-fl-f-+--H:-~-i-4- ...+-r.:--l-j-..l-+.. j~+-+-~..+-_-{I:-_._ ,._~~'~~=

-,-- l ' r--- t-'~ ~_.~- I- = ~~-J--l- +_I:'~..,.j-+-+-{I -I--I-~·_'--I-+4-1--+-II,·+-}--l~!""·I·~I-';"'+-1-·I-~--;--4~+41-j.o.-l-,~~~ I-I-~,- .- .. t I- f...- 1--. i- " ~ _-'" ~,_'-'t~~~;i;:- tl~~,,-.4.;'~-~-I~.'~'fiJ_~I'-+_I<'_--+-_~Ii'=-_~j~~~i~~i~~I:_~·;I·,·~;i~:,'~~:~: '::;_~!~--_~'-:-I ~.tl:-~_-~+---:-_-IJ--;~;·~-11---1;j--":I--4--1l-f h II f'." f-- I: l-f~1_ .- '\ 1 __ ~ ,-I-,~~-+-"'-li-t--J--l- .------r- \·...... f.--.+--I-II .....-I-+--I-- Ii t >- 1-· r:c ,,~ I- ~-'-r- _-ir·I.--.L-····I....L._~L.

1- 1- .., i___ ,n'~ ~ _ ~~r-;..~~~I-:'--:..-i-iI-+~tJ-!o+~-:--+-!-+-!-4H-r-~-++"=}=~-r+=~-t-1-i-~H~ ...... ll...... i~...... 1- ~n -j (1OOl:I

1--'-""1-~f-+·-+I-II.-+-.'H!-;'~--f~..-;'-+--1-'" -t-,t-f-+--t-i-+·-l-+-~i--l-+-+-+-~-+.-I-+~-11-i1-f--f""'-;-++---I-+-li-·:--t·--:-:-" ~ •• _. ~ ~ 1--+1--1-4-11·-1-l----+4·-1 -1-I-.I-+---II-l--H-HI---J-.-4--:-II--H·-t-+~I-I-r-.J-+.-"~!---":;"+·-I--~-!-I:-l-4-'-!-·,-~.;..--J-+-l--~l ~I ~-;. -I-l·-+·--l-~-I--r-+lr-·!--~ f!~ ~ ~ -~~ -- -.,-1_.+-.-1...... ;...... -1-_.[ . r----:i-!--I-f-l-'l"'.-+-·I··1-+-+-,- +-.. :-- .j. -t--D · ..... -1·->-·'--I - '_. '\ 1--'-'1' l~ --•.- oj --It-:---I--·+·-I-",r-t-'I-+-'~-l ~,-l--'l-'- t~: ·-1~';i--I1·-+~+-.f-f- ~.-I-i --1--+---11 :- f .) Ili~_l-_;'"_'~_-;'-ll""- '~·,'-'II ....;·.,.,~I-+-+-t-·;-lI-.--l-i-+-tt ~i"""'--l-.JI. -I--l-4-i,,-I--~--!·-+-~·-·i-· --.4 -t -+- -+,--,-+ r- ( U i 11]:" .-.-. ..1_'_ '-'- • f -.J ~ = --!-,~·-I~·-··i~' ~T- 11.-c:~.~-+-f-t---+-,f-_+:=~,.~-:~-:--=.l,-- I~== '_I_.'~ -..-:-l-l~r c-o- It' 'il +':-1' - '-'- I- J--.-. ::J .1-1. DISCUSSION OF RESULTS. The gloat fire of the bottom sagger reached cone 3, and along with this glost fire, the top sagger containing duplicate trials of both series resulted in a cone 2 fire. Series A.

The members No. 1,2 t 3, and 4 of series A in the bottorrl sagger (cone 3) had very little crystal~ille forraation. TIle glaze had a brown color and SOIne crys­ tal~ine growth was noted around the edges of the trials. These trials had the lowest amount of Fe203 (0.75 equi­ valents) ,and the E203 content varied from 1.25 equi­ valents for No.1 member to 2.00 equivalents for No.4 rnember.

The other members o~ the series showed a great amount of crystalline growth, with No.9, 10, 11, and 12 members showing the largest crystals. These members had a medium amount of ferric oxide (0.85 equivalents), and the B203 content varied from 1.25 equivalents for

No. g··member, to 2.00 equivalents for No. 12 member. When viewed under a mioroscope, the sturcture of the glaze resembled a mass of colored broken glass, but when exmnining a trial with a little crystalline growth, very definite crystals were seen • They were identified by Professor Muilenburg5 as hexagonal basal pinacoidal crystals of hematite. The crystals were of various colors. The members of series A in the top sagger (cone 2) showed the same characteristic as the members in the bottoln sagger (cone 3), with t11e exception that the crystalline growth was not as great. The crystals in members 15J~4J17J18t19Jand 20 were small, resembling small brassy particles.

The following graph shows the mernber s of aerie s A having the greatest crystalline growth. The cross hatching indicates the areas of greatest crystalline growth.

Graph No.1

0.75 1 2 4

0.80 Fe203 0.85

0.90 0.95

1.25 1.50 1.'15 2.00

B 0 2 3 (13)

Series B. The members of series B, in the bottom saggej (cone 3) that Showed the best crystalline growth were

No. 1,2,15,~6,19, and 20. The crystalline growth decreased in the members containing low ferric oxide content with the increas­ ing content of borax. The crystalline growth increased in the members of high ferric oxide content and with the increasing content of borax. TIle members that contained high ferric oxide and low borax content had very little aventurine affect. The had the same bro,~ color that was encountered in a few members of series A. Members No. 5,6,7,10,11, and 12, had a peculiar appearance. It seemed as if the gl~e had crazed and then annealed. The surface was perfectly smooth.

The cracking of the crystals t in trials which 11ad a very great crystalline growth, was caused by the unequal expansion and contraction of the hematite crys­ tals and the glass.

Graph No. II (on next page) shows the members of series B having the greatest crystalline growth. The cross hatChing indicates the areas of greatest crystall­ ine growth. (14)

Graph II

0.75 3 4

0.80 5 6 ? 8

Fe203 0.85 9 10 12 0.90 13 14

0.95 17 18

1.25 1.50 1.75 2.00

B 0 2 3 (15)

EFJfECT OF CONTROJ...IiliD COOLI1TG Rj~TJ~S 4} It was readily seen from the results of the inves­

tigation to date J that tlle control of the cooling en­ hances the growth of the aventurine crystals. The effect of controlled cooling rates on the crys­ talline growth was tried on member No.5 of series A. Fifteen trials were fired in an electric muffle.

Five tria~s were fired to cone W2, five to cone 1, and five to cone 3. The trials were drawn out at their respective temperatures.

Vmen cone 3 was reached, the cooling ~rocess was begun. The furnace was cooled at the rate of 30° Cent­ igrade per hour. Vllien the temperature, at which the trials of cone 1 were drawn out, was reached, the trials were returned in the furnace. The same was done with tne

trials of cone ii2. Trials were drawn at every hour, until the furnace had cooled to 9000 Centigrade. ( 16)

- ~~ I , ~ II-rT:;-"" ~ ,-, v- rT +--11 I --R:J. r·-!- ·f , 1._.1-1-;... ! ._-/--: ~ l- I- I !'+""1- ~ -~- I: ~m ~ :..... 11_ <»~ Et ~ :: '·-1-1- ~- ._~- -~~ ~t 1- 1-"1 .- () <> '0 T ~~~' ~.'iF'~~;!..:.~L~-~;*1r''':::;---'i.;=~=;'"'1-''''~~.J.~''''~~ "= ~ ~~ ~- ". 1- T~~~t!-p~vr ~ '""" :_ 4­ l'-,- L_I-

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,-1-.. -1-----­ ,-

l~ i r-·

iII---:i-!-"+"l---fe-j....-l""'""'~-j -;\-j I-~ _.. '-·I-I~-4-it·_·!-'-·I-l ....1I·~l-4--+--+···!I~·i-+...-f-·+-lI-· f­ l'\ , ::~ ~ ~~J-"""-I-"'-I--I-t ·i· l·-- !--' .. ~~-~-4...,..J •...f - 1-+-l-4--·_·1~+·+-·1--I ... ·1·~1 -~-l.-t-,~-,,"-! ~.-!-!- 1-+-f-+-lr--l·-I----1--f!-.. '--~~ -, I-I-c I- f--.- f_'-·f_ !-·1- - I- 1-' ~-

I.,... ._'._- ~ '.- f-'-~- 1--'- I - \0_' i.... fl · -,_ '1 f .. i- f- 'b t :.- I t= 8 I I _ ....J Iln=, t- : L._ .. - (17)

~

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I' ;-t-1-r-1-t--.. t-··, -,-1-)-+- ;-1I-1--I-+-l-lI-4-lf-4--l--IL__ ,'_--i1-{_. ~= !__ "~ ~ _.l-+-+-dJ-.~I-...l-l-Ji·- ",·--l-.l--!,-t--I-l--+-1-H-·-~f·_.:.,....j..-lj~-J.-l--4 _.~.T ·~~i~.f'!.--...i.~"'"i1 ,_ f _ ".. II _!"_I_-!-·l--!-_I/.-{ .--t-....-l·· •. _ll_\-_.;.. ;;:' I ~ 1,,_ I-V'/, --1 ~'-U·_~··t-r~~--I·~ H-I-·-H~~-rI-t".,-;-i:'-i>-'t·--t""'o.'·'-~H--l-·HH--J-t--t--I- ...I--;.....j·-+···44-~..J-+--1 ....).,..4--.1- I 1-,1- 1-\-;:--", I I~ 1- r-- . '·-1I·-+--+-!--+-ft -.- t-+-i~--I··,·/-.-+-1-1--t·_·H-·"I-·4-'II-+-I----I-i~I.-+-,J.-J.~J~..I

!._',,-

'~~-i .-.[.... .- .....f-·_j--i·~·-I.~.--I~ ;'..... \- I 1 t- - 1""-·1- 'I-...... _,._~._+I-._.:...... -_-~'•.. -. ,.,-_•.'"..,...... _..._.-4,1 ~.• ''-,_~ 1._ !d>·--,·,._-'II .•._1--,...; .. _;1.':-.~·_~I"·~·i--!--·!-.j.-~I-~!-:-If-4--l- tl-i-l-f-~-'I-i-+-+-~- ~ ,~. "-1-1- i- ;- - -

I ~_ L~'_'_. --I-

!•...;.- f-I-

:-- ~. ..'~.- -I-...... f-- "'r- ... I (18)

DISCUSSION OF RESULTS

Trials that were fired to cone 3. TIle first trial, drawn after one hour of cooling, showed little crystalline growth. A few ~~ystals were noticed around the edges of the trial. The trial drawn after two hours of cooling show­ ed a greater amount of crystals, and also larger cry­ sta~s.

Tl'le trial drawrl a.. fter four }lours of cooling sIlowed tile crystals gro'\ving in size and havir.i.g a mul­ titude of colors. The trial having five hours of cooling contained a large amount of multi-colorec crystals still grow-

One trial was allowed to cool in the furnace, and i.t contai11ed the greateat amount and c~lso the largest crystals.

Trials fired to cone 1.

The first trial that was drawn out llad a brassy color, and did not have any crystalline growth.

TIle second and third trials had a little crys~ talli!le growth, but the crystals were very small. (19)

The trial that had five hours of cooling had fairly lE.Lrge multi- colored crystals, while tl1e tria"l tha.t '\lv-as allovved to cool in the furnace showed an in­ crease in the size of crystals, but the trial was not yet completely covered with crystals. The edges of the trial did not have a crystalline formation.

Tria1s fired to cone 02. '!he first trial drawn did not have a crystalline growth" but the trial dnawn after two 110urs of cool­ ing showed a large number of very small multi- colored crystals.

The trial drawn after four hours of cooling con~ tained a large number of small brassy looking part­ icles or crystals, while the trial allowed to ~,oool with the furnace showed the crystals increa.sing in size, but the maximum crystalline growth not yet having been reached. (20)

CONCLUSIONS

It is concluded that:

1. Glazes having a low content of Fe203 (0.75 equivalents), and a low content of B203 (1.25 equiv­ alents), will give a small crystalline growth.

2. Glazes having a low content of Fe203 (0.75 equivalents), and a high content of B203 (2.00 equiv­ alents) J will give a slnall crystalline growtrJ.. 3. Glazes having a low amount of B203 (1.25 equive~lents), t:U1d a 11igh content of Fe203 (0.95 equiv­ alents), with a llic;ll silica COl'ltent (6.0 equival.erlts), will not give a goon aventurine effect. 4. Glazes giving the best aventurine effect con­ tain a moderate amount of FaZOS (0.85 equivalents), low or high content of borax or B203 (1.25 or 2.00 equiva.lents), and a low content of Si02 (5.0 equiv­ alents). 5. nle crystals have a definite crystalline shape. 6. The cracking of the crystals is due to the unequal expansion and contraction between the crystals (21)

7. A slow rate of cooling will give the great­ est crystalline growth and also results in larger crystals. RE COlill.ID1TDAT IONS•

};'or furtller work on t11is subject, it would be

advisable to study more thorOu~lly the effect of various controlled cooling rates on the crystalline

gro1vtll of tIle glaze, and a furtller study could. be made on the temperature a.t whiclJ. tile maximum aD.loWlt

of crystals, or wl'len tIle crystals l1ave stopped t};1'OW­ ing, is reacned, so that the kiln may be cooled rap­

id~y when the temperature reaches this point.

An extensive study could be made on agents that would suspend the glaze, so as to make spraying suit­ able for this type of glaze. The organic agents that could be tried as aids to the suspension of the glaze are:

1. Gum Arabic. 2. Gum Tragacanth.

3. Gum Karaya. 4. Dextrine. 5. Gelatine. Another method that could be tried is to add a strong ammonia solution to the glaze. (23)

APPLICATION TO THE INDUSTRY.

Due to tIle cost o:f rnateI'ials, tIle cost of frit­ ting, a~ld the trouble enCQUIltered in applying the glaze to the wure, makes this a glaze too expensive to apply to ordinary ware. Tllis glaze CQula. just 'ue used. i~o;" decorative art Vlare. (24) ,

.l1.. Cl~?TOV!LEDG~.ThJl~·T •

I wish to acknowledge t11€ kind assistance and practical advice rendered by' fur. A.~. P~ul

E~~ Professor C.M. Dodd of the ~eramic Depart~

Iilent, and Profefisor .G.A. Muilerlburg of tIle Geology Department. (26)

bI13LIOGRaPIIY

(1) W.R. Zimnler - crystallized G~azes T.A.C.S. Vol. 4, P. 3?, 1902.

(2) J. l~oerr.Ler - i~·ew Cr~tstQ.lll:Ee Glazes. T.A.C.S. Vvl. 10, P. 61, 1308

( ;;) ]'l •.l-I. Iiiddle -A Fev, j?c.ct S COlI ceI'lolirlg tIle 80- Galled

Zinc-Silicate Crystals

T.A.C.S. Vol. 8, P. 336, 1906.

(4) V.K.Haldenlarl - Avellturine Glazes.

J.A.C.S. ? (11) P. 824, 1924.

(5) G.A. MUilenburg - Professor of Geology, ~liSBOuri

School of Mines and lvIetallurgy. (26)

.AE~3TP.ACTS•

Notes on the Production of Crystalline Glazes.

Ray T. Stull. 'T.A.U.S. Vol 16, P. 186, 1904.

urystalline glazes may 1e divided into two classes t

(1) trlo se in which tJ:le crystals are produced by the so-called supersaturation method, and (2) ,glazes in wr.1.ich the entire mass 11&.8 a crystalline structure. The first class comprises the aventurine glazes as the tI Gold stone" or II Tiger-E~re". SUCll a glaze is produced by a mixture in which there is an exce-ss of one or lllore metallic oxides, or by applying these oxides to the body or bisque before dipping in the glaze. Upon firing, the glaze proper or glassy matrix liquifies. This liquid is capable of dissol­ ving more or less of the metallic oxide or oxides present. In cooling, the capacity of the glassy liq­ uid to hold its dissolved material in solution is lessened, hence the excess is deposited as crystals within a glassy matrix, or produces an opaque result due to incipient crystallization.

An e~eriment. was carried on to determine what ceramic materials gave to glazes the best tendencies to cl'ysto.,llize. T"ne resu..lts o:f~ tllese experiiient.:, ~,ee~.:ed to perlllit tIle follovving general cied.uct ions.

1. Tne ~:;t!&Ollgest crystalline tendencie s are

given to glazes by tl10se Cl1.elnical elements

of low atomic weight Whose oxides go to make

up tile R, ~3UCli as sodiwf.L, potassium, rnagnes...

ium, calci~, manganese, iron, zinc, etc.

2. Tl.iO e [ e tal S 0 f r.ligh a.t ami C ~le igllt, SUCIl as

bariwl, lead, etc., see 11 to ilIlpart a, glassy

nature to silic::ltes when used in sut"fi,j.cierlt

qUalJ.tities, w.riich is unfELvorable to crys­

tallization.

3. Thope chemical elerents of higher atomic

weigelt whose oxides ~ake the acid portion of

a glaze, Sllen as silicon, titanium, phosphor~

OUSt etc., produce the best cryEtallizing

agents, v~ile those of lower atomic weight,

floS for exaluple, 'bo on, haVing an atomic weight

of 1 , impart a fluidity and brilliancy to a

glaze which is detrimental to crystallization.

4. The introduction of an R20 lliaterially assists crystallization in some cases, hile in others

it is detrimental to it. Grystalline Glaz~s.

I' •.i .c.s. T 1 -d, ". ... 01 190?

ile aut:loII s eLi scuss various type s of crystalline­

glazes, and they state that of the two alkalies t pot­ ash and soda, the latte:r vvas f"ound to ~oe tlle rilO at conaucive to tne development of crystals.