Lime-Barium and Lime-Zinc Raw Glazes with Raw Materials from Tanzania and Cameroon

doi:10.4236/msa.2011.210188

Paper Menu >>

Journal Menu >>

Materials Sciences and Applicatio ns, 2011, 2, 1392-1398

doi:10.4236/msa.2011.210188 Published Online October 2011 (http://www.SciRP.org/journal/msa)

Lime-Barium and Lime-Zinc Raw Glazes with

Raw Materials from Tanzania and Cameroon

U. Chinje Melo1,2, Ndigui Billong1,2*, E. C. Kimaro3

1Materials Analysis Laboratory, MIPROMALO, Yaoundé, Cameroon; 2Physico-Chemistry of Mineral Materials Laboratory, Univer-

sity of Yaoundé I, Yaoundé, Cameroon; 3Industrial Minerals Laboratory, SEAMIC, Dar-es-Salaam, Tanzania.

Email: *[email protected]

Received March 1st, 2011; revised April 1st, 2011; accepted April 27th, 2011.

ABSTRACT

In the paper, the lime-barium and lime-zinc glazes used in Southern and Eastern Africa Mineral Center (SEAMIC) ce-

ramic unit in Tanzania were investigated for the production of high temperature raw glazes in Cameroon. The base

Seger formula used was 0.3KNaO, 0.3CaO, 0.4ZnO or BaO; xAl2O3 and ySiO2. Different Al2O3/SiO2 formula ratios for

glossy and matt glazes were tested with raw materials from Cameroon and Tanzania. In the Cameroonian glazes, a

local pegmatite (quartz, microcline, albite) with low coloured oxides replaced an albitic feldspar in the Tanzanian

glazes. The other materials were kaolin, limestone, silica and barium carbonate or zinc oxide. Th e glazes were tested at

Seger Cone 7 (1240˚C) on stoneware slabs (made up of the same feldspathic glaze material: 18%, silica sand or quartz

27%, ball clay 40% and kaolin 15%) from both Tanzania and Cameroon materials. From results obtained, zinc oxide

acted as a more vigorous flux than barium carbonate at cone 7, which is obvious in the glazes with pegmatite (with high

quartz content). At a Seger formula of Al2O3/SiO2 1:10, transparent glazes were obtained. In these glazes the alumina

content was lower and when increased to higher Seger ratios 1:4.7 - 8.7, the gloss was lowered to matt-luster due to

fine crystal formation.

Keywords: Lime-Zinc Gl azes, Lime-Bari um Glazes, Raw Glazes, Seger Cone 7

1. Introduction

Glazes constitute a fundamental material to the success

of the ceramic industry. During recent years, the de-

mands of shorter firing cycles and easy control of surface

microstructure have called for the use of fritted composi-

tions. Raw glazes have to a large extend been replaced by

fritted glazes. However, in the case of high temperature

ceramic products like tiles, stonewares and sanitarywares

fired at temperatures above 1200˚C, raw glazes are still a

competitive alternative to fritted formulations [1]. Glaze

is similar to glass but with a more complex system be-

cause it deals with more components; 7 or 8 oxides in

significant amounts are common [1-6]. These compo-

nents are divided into the glass network former (SiO2 or

B2O3), stabilizer (generally Al2O3) and flux or glass net-

work modifier or melter (R2O or RO, where R is an alka-

line, alkaline earth or fluxing metal). The complication

with glazes is accentuated by the fact that a thin layer is

applied to a ceramic body and the glaze body interaction

may result in faults. Such faults like cracks (at times

voluntary) can affect the aesthetics and technical proper-

ties of the product. A glaze is a mixture of materials,

powder or suspension in water which when applied as a

coating on a body and fired to an appropriate temperature,

vitrifies and develops specific properties. For every given

body composition, it is important to test the ideal glaze

based on aesthetics and properties envisaged.

This research was carried out to produce stoneware

glazes using Cameroonian raw materials, to replace

costly imported stoneware and porcelain glazes com-

monly used in Cameroon. The studies were carried out at

SEAMIC in Tanzania, investigating the base glaze com-

positions used on its decorative stoneware products.

These high temperature glazes are of lime-barium (bar-

ium glazes) and lime-zinc systems and are raw, not using

fritted materials or lead. Barium glazes are recommended

for their ability to produce brilliancy and hardness [7].

The base Seger formula for the glazes was 0.3KNaO,

0.3CaO, 0.4ZnO or BaO; x Al2O3 and y SiO2 at cone 7

(1240˚C). The x/y (Al2O3/SiO2) ratio has been reported

to have a great influence on the glaze surface as indicated

n igure 1 [2,3,8,9]. i

Lime-Barium and Lime-Zinc Raw Glazes with Raw Materials from Tanzania and Cameroon1393

Figure 1. Variation of x (Al2O3) and y (SiO2) molecular formula for glaze preparation.

2. Experimental

2.1. Raw Materials

Raw materials used in Tanzanian glazes (TG) were

available in SEAMIC and are given in Table 1. Included

are those for Cameroonian (CG) glazes, indicating their

sources. Chemical compositions were analysed by x-ray

florescence, fused bead method with a SIEMENS SRS

3000 spectrometer. Mineralogical analyses were carried

out with a SIEMENS D 5005 diffractometer.

2.2. Experimental Procedure

2.2.1. Glaze Form ulation

Molecular ratios of Al2O3 and SiO2 were varied to pro-

duce glossy glazes with single glass phase glossy (zone

A) and matt glazes with fine crystals (zone B) using Fig-

ure 1. Molecular Al2O3/SiO2 ratios 1:10 for A zone and

1:4.6 - 8.7 for the B zone were tested. Tables 2 and 3

indicates different ratios of x and y tested for Tanzanian

glazes and Cameroonian glazes. The glaze recipes were

calculated with these assumptions: that limestone, kaolin,

and silica sand (flint) were pure, of respective composi-

tion CaCO3, Al2O3·2SiO2·2H2O and SiO2; and that feld-

spathic materials (feldspar and pegmatite) were mixed

feldspar of composition KNaO·Al2O3·6SiO2.

2.2.2. Glaze Prepa ration a nd Applic ation

As received materials (flint, quartz, feldspar, limestone

and pegmatite) were crushed in a DIETZ jaw crusher to

<400 µm and dried at 105˚C for 24 hours. The glaze

recipes were composed using a Sartorius V3600S (max

load 3640 g and sensibility 0.1 g) scale. 45% water was

added to the raw glaze mixture which was then ball

milled until all passed a 75 µm sieve. Densities were

adjusted to about 1550 g/L using a Baume hydrometer.

Table 1. Raw materials and their source.

Materials Source

Pegmatite Mont Nlonako, Littoral Region, Cameroon

Kaolin C Mayoum, Foumban, West Region, Cameroon

Quartz Mvan, Yaoundé, Center region, Cameroon

Clay C1 Mvan, Yaoundé, Center Region, Cameroon

Clay C2 Bambili, North-West Region, Cameroon

Feldspar SEAMIC, Tanzania

Kaolin T SEAMIC, Tanzania

Flint T SEAMIC, Tanzania

Limestone T SEAMIC, Tanzania

Clay T SEAMIC, Tanzania

Zinc oxide SEAMIC, Tanzania

Barium carbonateSEAMIC, Tanzania

Lime-Barium and Lime-Zinc Raw Glazes with Raw Materials from Tanzania and Cameroon

1394

Table 2. Tanzanian glaze (TG) recipes and Al2O3/SiO2 molecular ratios.

Recipe (wt%)*

Glaze x y Al2O3/SiO2 (Seger) F K (T) L Fl Zn Ba

Glaze system

TG1 0.30 3.0 1:10 54.6 n.u. 10.1 24.3 11.0 n.u. Ca-Zn

TG2 0.30 3.0 1:10 47.2 n.u 8.8 21.0 n.u. 23.0 Ca-Ba

TG3 0.35 3.5 1:10 42.4 3.4 7.9 25.3 20.0 20.8 Ca-Ba

TG4 0.40 4.0 1:10 38.9 6.2 7.2 28.8 n.u. 18.9 Ca-Ba

TG5 0.65 3.0 1:4.6 47.0 26.2 8.7 8.7 9.4 n.u Ca-Zn

TG6 0.65 3.0 1:4.6 41.4 23.1 7.7 7.7 n.u. 20.2 Ca-Ba

TG7 0.45 3.0 1:6.7 44.6 10.6 8.3 14.9 n.u. 21.7 Ca-Ba

TG8 0.65 5.0 1:7.7 31.7 17.7 5.9 29.4 n.u. 15.4 Ca-Ba

*F = Feldspar; K(T) = Kaolin; L = Limestone; Fl = Flint (silica sand); Zn = ZnO, Ba = BaCO3; n.u. = not used in recipe.

Table 3. Cameroonian glaze (CG) recipes and Al2O3/SiO2 molecular ratios.

Recipe (wt%)*

Glaze x y Al2O3/SiO2 (Seger) P K (C) L Q Zn Ba

Glaze system

CG1 0.30 3.0 1:10 54.7 n.u. 10.1 24.3 10.9 n.u. Ca-Zn

CG2 0.40 4.0 1:10 38.9 6.2 7.2 28.8 n.u. 18.9 Ca-Ba

CG3 0.40 4.0 1:10 44.0 7.0 8.0 32.0 9.0 n.u. Ca-Zn

CG4 0.35 3.0 1:8.6 46.3 3.7 8.6 18.9 n.u. 22.5 Ca Ba

CG5 0.45 3.0 1:6.7 44.5 10.6 8.3 14.9 n.u. 21.7 Ca Ba

CG6 0.50 3.0 1:6.0 43.7 13.9 8.1 13.0 n.u. 21.3 Ca Ba

CG7 0.50 3.0 1:6.0 48.0 15.0 9.0 18.0 10.0 n.u. Ca Zn

CG8 0.35 3.5 1:10 56.7** n.u. 8.7 24.9 9.6 n.u. Ca - Zn

*P = Pegmatite; K = Kaolin; L = Limestone; Q = Quartz; Zn = ZnO; Ba = BaCO3; n.u. = not used; **Pegmatite was replaced by the fusible clay C2.

Slips were applied by dipping method on unfired stone-

ware body.

2.2.3. Stonewa re Body C om p osi tion

The Tanzanian glazes were applied on a body using raw

materials from Tanzania. Similarly, Cameroonian glazes

were applied on a body made up of local materials from

Cameroon. The Tanzanian ceramic body was made up of

18% feldspar T, 27% flint T, 40% clay T and 15% kaolin

T and that of Cameroonian 18% pegmatite C, 27% quartz

C, 40% clay C1 and 15% kaolin C. The stoneware body

test pieces were produced by crushing the raw materials

with water in a ball mill and filter pressed to remove ex-

cess water. The paste obtained was flattened on a roller,

and slabs cut for glaze trials.

2.2.4. Firing Sc hedules

The glazed test pieces were single fired on Seger cone 7:

1240˚C, in a Linn Electrotherm electric kiln. From am-

bient temperature to 650˚C, the firing rate was 2.71˚C/

min, and from 650˚C to 1240˚C, 2.46˚C/min. The test

pieces were soaked at 1240˚C for 2 hours and were al-

lowed to cool in the kiln to ambient temperature before

removal.

3. Results and Discussion

3.1. Chemical and Mineralogical Compositions

of Raw Materials

The results of chemical composition determinations on

Tanzanian and Cameroonian raw materials are given in

Tables 4 and 5 respectively. The feldspar is more sodic

and the pegmatite more potassic. The percentage of

non-feldspathic components in these materials is quite

low. The high SiO2 content of pegmatite is expected to

alter the melting behaviour as compared to feldspar,

when the recipe contains the same amount of feldspathic

Lime-Barium and Lime-Zinc Raw Glazes with Raw Materials from Tanzania and Cameroon1395

Table 4. Chemical composition (wt%) of Tanzanian raw materials.

Oxide Silica sand Feldspar T Kaolin T Limestone T Clay T

SiO2 97.58 65.18 49.60 5.25 51.28

Al2O3 1.41 20.70 35.76 2.03 30.14

Fe2O3 0.19 0.10 1.07 0.99 1.69

MnO <0.01 <0.01 <0.01 <0.01 <0.01

TiO2 0.31 <0.01 0.40 <0.01 0.31

MgO 0.05 0.12 0.11 0.41 0.41

CaO 0.18 1.40 0.09 49.70 0..41

Na2O 0.06 8.70 0.17 0.40 0.61

K2O <0.01 2.61 0.19 <0.01 2.00

P2O5 <0.01 <0.01 <0.01 <0.01 <0.01

L. O. I. 0.20 0.41 12.58 40.70 13.04

Total 99.98 99.22 99.97 99.48 99.89

Table 5. Chemical composition (wt%) of Cameroonian raw materials.

Oxide Quartz Pegmatite Kaolin C Clay C1 Clay C2

SiO2 99.02 82.55 45.12 60.02 71.71

Al2O3 0.40 8.93 34.59 27.83 12.86

Fe2O3 0.22 0.52 1.25 2.17 2.86

MnO <0.01 0.03 <0.01 <0.01 0.03

TiO2 <0.01 0.03 4.76 1.15 0.19

MgO 0.15 0.28 0.35 0.56 0.26

CaO <0.01 0.38 <0.01 <0.01 0.35

Na2O 0.17 2.05 0.15 0.22 0.74

K2O <0.01 4.85 0.13 0.39 3.90

P2O5 <0.01 <0.01 0.33 0.39 <0.01

L. O. I. 0.03 0.08 13.15 7.08 6.83

Total 99.99 99.70 99.83 99.81 99.73

material. Both kaolin T and C contain about 35% Al2O3

and iron content within the stoneware composition. The

presence of 4.76% TiO2 in kaolin C resulted in stoneware

with a darker colour. The limestone contain 89% CaCO3,

with main impurities SiO2 and Al2O3 and low MgO. The

quartz stones are of very high purity.

From x-ray analyses, pegmatite contained quartz, al-

bite and microcline; clay C1 quartz and kaolinite; and

clay C2 a very fusible clay (fusion point 1200˚C): kao-

linite, montmorillonite, quartz and microcline. Kaolin C,

from previous analysis [10] is made up essentially of

kaolinite and quartz with traces of illite, anatase and an-

orthite. Clays T and C1 are ball clays for stoneware bod-

ies.

3.2. Glazed Test Pieces

The visual appearance of the glazed test pieces are de-

scribed in Tables 6 to 8 in which the glaze systems, SiO2

and Al2O3 contents, are included.

TG1-TG4 gave glossy transparent glazes (Table 6).

The Al2O3/SiO2 molecular ratio is 1:10. TG1 is a Bristol

glaze and is colourless, whereas the barium glazes TG2-

Lime-Barium and Lime-Zinc Raw Glazes with Raw Materials from Tanzania and Cameroon

1396

Table 6. Visual appearance of TG and their silica and alumina contents.

Surface structure

Glaze SiO2 wt% A l2O3 wt% Glaze system Colour Appearance

TG1 59.9 11.3 Ca-Zn colourless high gloss, transparent, smooth feel, no craze

TG2 51.8 9.8 Ca-Ba light khaki high gloss, coloured, smooth, crazed

TG3 54.8 5.5 Ca-Ba light khaki high gloss, coloured, smooth, crazed

TG4 45.9 10.5 Ca-Ba light khaki glossy, coloured, no crazing, fine bubbles, rough feel

TG5 52.3 19.1 Ca-Zn white high gloss, opaque, no crazing

TG6 46.1 16.8 Ca-Ba pastel beige opaque, matt, no crazing

Table 7. Effect of colorants on Tanzanian glazes.

Surface structure

Glaze Description Glaze system Colour Appearance

TG7 TG7 + 5% MnO2 Ca-Ba purple + whitish specks low gloss, opaque, no crazing, smooth feel

TG8 TG8 + 5% MnO2 Ca-Ba yellow-brown glossy ,opaque, no crazing

TG9 TG6 + 5% MnO2 Ca-Ba dark brown opaque, matt, no crazing

TG10 TG6 + 5% Fe2O3 Ca-Ba chocolate brown opaque, matt, no crazing

TG11 TG6 + 1% CoO Ca-Ba blue opaque, matt, no crazing

TG12 TG6 + 2% NiO Ca-Ba pale pink opaque, matt, no crazing

TG13 TG6 + 2% Cr2O3 Ca-Ba dark brown opaque, matt, no crazing

TG14 TG1 + 2% Fe2O3 Ca-Zn brown glossy, opaque, no crazing

TG15 TG1 +1% CoO Ca-Zn deep marine blue high gloss, opaque, no crazing

Table 8. Visual appearance of Cameroonian glazes and their silica + alumina contents.

Surface structure

Glaze SiO2 wt% Al2O3 wt% Glaze system Colour* Appearance

CG1 74.0 8.4 Ca-Zn whitish incomplete fusion

CG2 65.7 5.7 Ca-Ba colourless Glossy, transparent, no crazing

CG3 71.4 6.3 Ca-Zn colourless Glossy, transparent, no crazing

CG4 58.7 5.4 Ca-Ba colourless Opaque, matt, no crazing

CG5 56.4 7.7 Ca-Ba whitish Opaque, matt, fine crazes

CG6 55.3 8.71 Ca-Ba colourless Glossy, transparent, no crazing

CG7 64.4 9.5 Ca-Zn colourless Glossy, transparent, no crazing

CG8 65.5 7.3 Ca-Zn yellow Opaque, matt, no crazing

*The stoneware body fired to beige, consequently mild coloration could not be perceived.

TG4 possess a light khaki tint. Decreasing BaCO3, a

fluxing agent, reduces the glossiness. In the BaO-CaO-

SiO2 ternary phase diagram, a liquid phase exists at as

low as 1268˚C [10]. This eutectic contributes to the low

temperature phases obtained at cone 7. Omar et al. [11],

observed that to introduce glass-ceramics into industrial

Lime-Barium and Lime-Zinc Raw Glazes with Raw Materials from Tanzania and Cameroon1397

applications, crystallizing agents had to be added to Ba-

aluminosilicate glasses. With high BaCO3 contents: 23%

in TG2 and 21% in TG3, the glazes showed mild crazing,

probably due to the high dilatation coefficient of BaO, in

addition to the high amount of alkaline feldspar. The

dilatation coefficient of BaO is 3.0 × 10−7/˚C in fritted

glazes but can attain 6.0 × 10−7/˚C in raw glazes [12].

The thermal expansion in these glazes could be lowered

by reducing the alkali content, that is, the feldspar con-

tent [2,8,13]. ZnO showed a vigorous fluxing action

(TG1, 11.0% ZnO) when compared to BaO (TG2, 16%

BaO) for the same Al2O3/SiO2 molecular ratio, 1:10. In

the ZnO-Al2O3-SiO2 ternary phase diagram, low tem-

perature compounds were located at the poor Al2O3 and

high (above 50%) SiO2 ends [10]. In TG5 Bristol glaze, a

white opacification occurred. ZnO which forms the basis

of Bristol glazes has been noted to increase whiteness,

especially in zircon glazes. At low Al2O3/SiO2 molecular

ratio 1:4.6 (high amount of Al2O3), opacity is probably

due to very fine crystals of zinc compound(s), such as

gahnite, ZnO·Al2O3.

The barium glaze TG6, with Al2O3/SiO2 molecular ra-

tio 1:4.6, is the base matt glaze in SEAMIC’s ceramic

unit. It has been reported that low barium release (non

toxic) could be obtained with up to 20% barium, when

the Al2O3 + SiO2 content is high, i.e. above 75% [14]. In

this matt lime-barium glaze, the barium content was 14%

and the Al2O3 + SiO2 63%. For the other barium glazes

tested, the barium contents were between 10.7% and

16.0% with Al2O3 + SiO2 content between 60% and 56%.

It is important to study barium release for these glazes

when use in dinner ware industry is envisaged.

Comparing the Al2O3/SiO2 molecular ratios of the

glazes, for Bristol glazes, 1:10 ratio (TG1) gave trans-

parent glaze and opacity developed when varied to 1:4.6

(TG5). This confirms the widely accepted Figure 1 and

observations that the x-y ratio has a great influence on

glaze surface. In Table 6, it is noted that this is directly

related to the Al2O3 content; 11.3% Al2O3 in TG1 and

19.1% in TG5. The same is true for the barium glazes;

TG2-TG4 of 1:10 molecular ratio are transparent with <

10.5% Al2O3 and a matt glaze is obtained with formula

1:4.6, containing 16.8% Al2O3. Transition metal oxides,

when added raw, give colour upon firing of ceramic

glazes. The colours obtained with MnO2, Fe2O3, CoO,

NiO and Cr2O3 are indicated in Table 7. TG7, TG8 and

TG9 (base TG6) all barium glazes contain 5% MnO2.

TG7 is matt and purple; TG8 is of low gloss, fine bub-

bles and brown, while TG9 is of low gloss, and dark

brown. MnO2 generally gives brown but in high alkali

glazes, fires to purple [8]. TG7 with the highest feldspar

content (45%) fired to purple, while TG9 (base TG6) and

TG8 containing 42% and 32% feldspar respectively,

gave brown hues. 5% Fe2O3 gave a matt chocolate-brown

on barium base glaze TG6, i.e. TG10; while 2% Fe2O3 on

Bristol base glaze TG1 (i.e. TG14) gave a high gloss pale

brown glaze.

With 2% NiO, the barium base TG6 glaze gave pale

pink (TG12). 2% Cr2O3 produced a brown coloration on

barium base TG6 glaze. The refractoriness of Cr2O3 was

obvious as this glaze TG13 did not fuse completely. 1%

CoO on both barium and Bristol base TG6 and TG1

glazes gave respectively a matt blue TG11 and high gloss

and strong ultramarine coloration, TG15. Cobalt is a very

powerful colorant which easily dissolves in glaze matrix

(with fluxing action) and enters the structure [8]. Cobalt

colours tend to be brighter in Bristol glazes whereas iron

colours are duller [4].

Cameroonian glazes CG2 and CG3, Table 8, respect-

tively for barium and Bristol glazes with Al2O3/SiO2

molecular ratio 1:10 were uncoloured, transparent and of

high gloss. These surface structures were similar to Tan-

zanian glazes with same ratio. These glazes can serve as

base glazes for transparent stoneware using Cameroonian

local materials. Barium glaze CG6 and Bristol CG7 of

ratio 1:6 were of mild gloss and showed some opacifica-

tion. This was probably due to the formation of very fine

barium or zinc aluminosilicate compounds. CG1 of Bris-

tol glaze series presented an incomplete fusion at cone 7.

The insufficient fluxing action of the 11% ZnO was

probably due to the high quartz content: 82% SiO2 in

pegmatite (54.7% in the recipe). An increase in tempera-

ture to a higher cone, >1240˚C is required. It is worth

observing that with 54.6% feldspar in the Tanzanian

glaze TG1, a single glass phase was obtained at cone 7.

This implies that ZnO had a higher fluxing action on the

feldspar (Tanzanian) than on the pegmatite (Cameroo-

nian). At lower pegmatite content, 44% in the recipe, the

fluxing action of 9.0% ZnO is evident in CG3. Some

opacification gave a mid matt glaze in CG4 barium glaze

(Al2O3/SiO2 molecular ratio 1:8.6). A matt glaze was

obtained with CG5 of ratio 1:6.7. Both CG4 and CG5 are

recommended as base glazes for coloured Cameroonian

matt glazes. Clay C2 of high fusibility (melts at 1200˚C)

replaced pegmatite in glaze CG8. A yellow opacification

was obtained on a matt surface. This clay could be ex-

plored in the production of glazes in Cameroon. On the

recommended base glazes for transparent (CG2 and CG3)

and matt glazes (CG4 and CG5), detail investigation of

the effect of colorant transition metal oxides should be

carried out when required by exploring the results on the

Tanzanian glazes.

4. Conclusions

Cameroonian materials (pegmatite, kaolin, quartz and

limestone) can be used in raw lime-barium and lime-zinc

Lime-Barium and Lime-Zinc Raw Glazes with Raw Materials from Tanzania and Cameroon

1398

(Bristol) glazes at cone 7 on stoneware when fritting is

not possible. The base Seger or molecular formula was

0.3KNaO, 0.3CaO and 0.4ZnO or BaO; x Al2O3 and y

SiO2. The influence of Al2O3/SiO2 molecular formula

that is x-y variation on the glaze surface structure was

evident on both the Tanzanian and Cameroonian glazes.

Ratio 1:10 gave transparent glazes and 1:4.6 - 1:8.7 mid

matt to matt glazes. The latter, a result of very fine crys-

tal formation. Transparent glazes contained lower amounts

of Al2O3 than matt glazes, alumina therefore influenced

crystallization.

Different hues were obtained upon addition of metal

oxides MnO2, Fe2O3, Cr2O3, NiO and CoO on the base

glazes for both transparent and matt glazes. The glaze

recipe and system (lime-barium or lime zinc) influenced

the colour and the surface structure for the same colorant

metal oxide.

REFERENCES

[1] L. Fröberg, T. Kronberg and L. Hupa, “Effect of Soaking

Time on Phase Composition and Topography and Surface

Microstructure in Vitrocrystalline Whiteware Glazes,”

Journal of the European Ceramic Society, Vol. 29, No.

11, 2009, pp. 2153-2161.

doi:10.1016/j.jeurceramsoc.2009.01.012

[2] W. James and A. W. Norris, “Some Physical Properties of

Glazes,” Transactions and Journal of the British Ceramic

Society, Vol. 55, 1956, pp. 601-630.

[3] H. Norster and J. Danish, “Glazes-for the Self-Reliant

Potter,” GATE, Vieweg Publication, 1987.

[4] R. Behrens, “Glaze Projects—A Formulary of Leadless

Glazes,” Ceramics Monthly Magazine Handbook, Profes-

sional Publications, Belmont, 1992.

[5] Th. Rehren, “A Review of Factors Affecting the Compo-

sition of Early Egyptian Glasses and Faience: Alkali and

Alkali Earth Oxides,” Journal of Archéological Science,

Vol. 35, No. 5, 2008, pp. 1345-1354.

doi:10.1016/j.jas.2007.09.005

[6] H. Desirena, A. Schűlzgen, S. Sabet, G. Ramos-Ortiz, E. de

la Rosa and N. Peyghambarian, “Effect of Alkali Metal

Oxides R2O (R = Li, Na, K, Rb, and Cs) and Network in-

termediate MO (M = Zn, Mg, Ba and Pb) in Tellurite

Glasses,” Optical Materials, Vol. 31, No. 6, 2008, pp. 784-

789. doi:10.1016/j.optmat.2008.08.005

[7] J. Malins and K. H. Tonge, “Reduction Lustre Glazes and

Pigments,” British Ceramic Transactions, Vol. 92, No. 2,

1993, pp. 83-88.

[8] J. R. Taylor and A. C. Bull, “Ceramic Glaze Technology,”

Pergamon Press, New York, 1986.

[9] E. Tejiogap, “Etude de l’Action du Fluorure de Potassium

sur Quelques Argiles Camerounaise du Groupe de la

Kaolinite,” PhD Thesis, Université de Yaoundé I, Yaoun-

dé, 1996.

[10] E. M. Levin, H. F. McMurdie and F. P. Hall, “Phase Dia-

gram for Ceramists,” American Ceramic Society, Co-

lumbus, 1956.

[11] A. A. Omar, A. W. A. El-Sheunawi and G. A. Khater,

“The Role of Cr2O3, Li and Their Mixtures on Crystalline

Phase Formation and Microstructure in Ba, Ca, Mg Alu-

minosilicate Glass,” British Ceramic Transactions and

Journal, Vol. 90, No. 6, 1991, pp. 179-183.

[12] C. Vittel, “Pâtes et Glaçures Céramiques,” Edition Delta

SA, CH-1800 Verey, 1986.

[13] J. E. Marquis and R. A. Eppler, “Leadless Glazes for

Dinnerware,” American Ceramic Society Bulletin, Vol. 53,

No. 5, 1974, pp. 443-449.

[14] J. Deboos, “Living Dangerously: Barium Glaze Research

Project,” British Ceramic Transactions, Vol. 98, No. 1,

1999, pp. 35-38. doi:10.1179/096797899680228