The document summarizes the development of lead-free frit to replace lead compounds in ceramic glazes due to the toxic effects of lead poisoning. Boric acid and borax were found to be effective and economical replacements for lead oxide, as borate compounds increase the fluxing action of glazes without impairing quality. A series of 13 lead-free frit formulations were prepared with varying contents of silica, sodium oxide, and boric oxide. Frit number 10, containing 61.4% silica, 8.1% sodium oxide, and 15.7% boric oxide, was determined to be optimal as it matured at 1050°C without crazing or other defects when applied to ceramic

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© (2014) Copyright ORIC Publications
Journal of Chemistry and Materials Research
Vol. 1 (4), 2014, 108111
JCMR
Journal of Chemistry and
Materials Research
ORICPublications
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Original Research
Development of Lead‒Free Frit to Get Rid of Lead Poisoning
M. Saadet Khan, Phool Shahzadi *, Khalid Javed, Akhtar Shahnaz, M. Usman Alvi, Javed Naqvi, Abdul
Ghaffar and Sajjad Hassan
Glass & Ceramics Research Centre, Pakistan Council of Scientific and Industrial Research Laboratories, Ferozepur Road, Lahore-Pakistan
University of engineering and technology,Lahore, Pakistan Department of chemistry,Minhaj University Township, Lahore-Pakistan.
Received 20 August 2014; received in revised form 27 September 2014; accepted 07 October 2014
Abstract
Due to poisonous nature of lead, it is totally replaced by borate compounds without impairing the quality of glazes. Borate compound increases
fluxing action. Borax and boric acid are the most effective and economical raw materials for introducing B2O3 into frit. Borate glazes are used
for the production of pottery, wall and floor tiles, stove tiles, bricks, roofing tiles, table wares and sanitary wares etc.
Key words: Lead free frit; Borate compounds in glazes; Use of lead free frit in household.
1. Introduction
Lead has been used in ceramic glazes from ancient times
and its use confers low melting temperature and low viscosity
in the molten glaze. Due to the fluxing and refractive proper-
ties for lead glass also make it attractive as a pottery or ceramic
glaze [1]. Lead glazes first appear in first century BC to first cen-
tury AD Roman wares, and occur simultaneously in China. They
were very high in lead, 45–60 % PbO, with very low alkali cont-
ent, less than 2 % [2]. Lead is an important network modifier in
glass network structure of lead containing glazes. It has strong
solvent action. Lead glazes give brilliant smooth finishes due
to its high refractive index and the glaze has a wide margin of
safety in firing. Because the oxides of lead are heavy and have
a granular structure, they tend to settle out of water quickly,
white lead, the basic carbonate 2PbCO3, Pb(OH)2 has flaky
structure which suspends well in water. Consequently, it was
widely used. As the oxides and basic carbonate of lead are
soluble in the hydrochloric acid contained in the gastric juices,
they were a potential source of lead poisoning.
* Corresponding author. Tel.: +03347586840.
E-mail address: psk_a@yahoo.com (P. Shahzadi).
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Lead poisoning can be carried out through the mouth by
breathing vapor or lead dust or through cuts. It is difficult to
cure, once it is taken into the system. Lead poisoning results
from the accumulation of lead in human body. Even small
compounds taken in daily over a period of years will reach a
critical level. It causes kidney failure and many other diseases.
Because of the chance of lead poisoning, however, lead
compounds are no now used in commercial glazes. Poisonous
nature of lead is that even after being fired some lead glazes
are soluble in acids which can get into the food from the dishes
so, because of danger of lead poisoning lead compounds are
not used in commercial glazes now.
To get rid of lead poisoning, factory regulations should be
framed to reduce the possibility of lead containing dust
entering the body, second consideration should be given to
avoid the use of lead in glazes and third consideration is to
reduce the lead compounds insoluble in the gastric juices.
Thorpe examined the effect of composition of lead frits on
solubility in 25 % HCI acid this being taken as equivalent to
the strength of acid in gastric juices at body temperatures. The
other drawback is that lead frit is slight yellow in color; this
yellow tinge affects other color and which are added to lead
glazes, sometimes spoiling their effect. Lead glazes are
mechanically soft and also have the tendency to dullness in
sulfurous atmospheric condition. They are also sensitive to
reducing gases produced during melting.
It is also found that introduction of alumina greatly reduce
the solubility of lead mono ‒ silicate and alumina is reducing

2. M. Saadet Khan et al. / Journal of Chemistry and Materials Research 1 (2014) 108–111 109
solubility oflead is more powerful than silica. But infect itisneed
of the time to replace lead compounds with other fluxes. The
common fluxes which are usually considered as replacement
for lead oxide are boron, barium, strontiumand zinc compounds.
Among theseboroncompoundlike boric acid and borax are most
suitableforreplacementofPbO.The present studyis based on the
inclusionofB2O3 forthecompletereplacementofPbOinglazes.
When lead oxide is not used we have to rely on basic
oxides like calcium oxide, magnesium oxide and the alkali
oxides such as Na2O, K2O & Li2O for fluxing together with the
powerful fluxing effect of B2O3. Since alkali oxides contribute
a high expansion to the glaze and therefore, the amount which
can be used is limited if crazing is to be avoided on the normal
pottery bodies [3]. CaO therefore becomes an important flux.
This in turn brings difficulties since large amounts of CaO tend
to give a best fluid melt. Moreover, calcium silicate tends to
crystallize readilyfromthe melt, and to prevent this, the amount
of Al2O3 must be increased. This increases the viscosity of the
molten glaze which is undesirable when leadless earthenware
type glazes are used they have some advantages, especially as
they tend to give a whiter glaze than leas ones. On the other
hand, they suffer from lack of fluidity in the molten state and
losses from pin holes, blister and dimples are more prevalent
than with lead glazes [4]. Leadless borate is also in general
less resistant to the action of acids, alkalis and weathering,
there is also less latitude in firing. A large preparation of the
glaze is normally fritted to reduce the danger of pin holes.
Frits are widely used in different industries like frit ware
knownaspottery[5].Andaretypicallyintermediatesintheproduc-
tion of raw glass, as pigments to enamels on steel pipes [6].
Powderedfritscan be usedasscaffolds for bone substitutions [7].
For introducing boric oxide into ceramic glazes the
following compounds and minerals are used.
1.1.Boric acid and sodium tetraborates
The main sources of introduction of B2O3 in glazes are
boric acid & borax. Boric acid (H3BO3) is volatile and water
soluble. On heating to 105 °C it loses water molecule and
becomes meta‒boric acid, upon further heating to above 160
°C the meta‒boric acid changes into tetra-boric acid (H2B4O7)
which when calcinated yields a glassy, molten mass of boric
oxide. Free boric acid occurs in nature as mineral sassolite.
Boric acid is used in glazes when alkali oxides are unwanted.
Boric acid contains 56.3 % B2O3. Borate compounds and
minerals are used for simultaneously introducing boric oxide
and alkali or alkaline earth oxides into ceramic glazes. Usually
the minerals are purified give pure borate products.
1.2.Sodium tetraborate decahydrate (BORAX).
(Borax)Na2B4O7. 10H2O appears in nature as various
minerals. When heated at 400 °C borax gives off all its
constitutional water and at 74 °C forms a glassy melt. Borax is
hygroscopic, water soluble and used only in fritted glazes.
Substituting boric oxide for a portion of the silica content is a
sure means of reducing the melting temperature of the glaze
without danger of devitrivification. Borax contains 36.52 %
B2O3 and 16.25 % Na2O.
2. Procedure
Quality raw materials are required for the production of
quality frits. Grain size ‒ 40 to ‒ 60 is better for frit melting.
Since smaller grains and larger surface areas represent lower
melting temperatures and higher melting speed [8]. Refractor
substances such as quartz and feldspar should not be finer than
‒200 mesh size. Main raw materials required are quartz,
feldspar, borax, boric acid, soda ash, aluminum oxide,
potassium nitrate, limestone and kaolin etc. All raw materials
used were commercial grade. All batch components were well
mixed in ball mill. Leadless frits have no fixed meting points
during heating, but utilizing a reasonable meting temperature
and time frame atmosphere is critical for frit quality. If a too‒
low melting temperature is used, insufficient frit melting can
lead to numerous flaws. But excessive high melting temperature
for long period can lead to the volatilization of fusible
components, such as borax boric acid and sodium bicarbonate.
Generally melting temperature for leadless glazes may vary
from 1450 to 1550 °C, depending upon composition [9]. All
melting’s was carried out in clay crucibles. One kilogram
batch of each composition was prepared and melted at a
temperature mentioned above for 3 to 5 hours. After complete
melting the molten glass is poured in cold water. The molted
glass is shattered is like small grains. This shattered glass is
called frit which is dried and ground to – 300 mesh. 5 % china
clay was added in this during grinding. Then by adding water
glaze slip was prepared. All frit samples were prepared in the
same manner. The experimental bodies whose composition
was red clay 80 % quartz 20 % were fired at 900 °C to make
the bisque. The glaze slips of all compositions were applied on
bisque by spraying. The bodies were dried in oven. The dried
pieces were then fired in electric furnace at different
temperature from 800‒1050 °C because different compositions
have different maturing temperatures [10].
3. Results and Discussion
A standard lead frit was selected for study as shown in
table 2.i.e. frit No.1. Frit 1 is totally replaced by Na2O as
shown in frit No.2. Form frit No.3 to frit No. 8 Na2O is
gradually reduced while B2O3 is gradually increased at same
ratio. From frit No.9 to 13, B2O3 is kept constant i.e. 15.7 %
while Na2O is gradually reduced and SiO2 is gradually
increased at the same rate. All frits were applied on a body
whose composition and chemical analysis are known.

3. 110 M. Saadet Khan et al. / Journal of Chemistry and Materials Research 1 (2014) 108–111
Table 1. Composition of frits
S # SiO2 Na2O Al2O3 PbO K2O CaO B2O3
1 59.4 3.1 5.5 21.0 1.8 5.5 3.7
2 59.4 24.1 5.5 0 1.8 5.5 3.7
3 59.4 22.1 5.5 0 1.8 5.5 5.7
4 59.4 20.1 5.5 0 1.8 5.5 7.7
5 59.4 18.1 5.5 0 1.8 5.5 9.7
6 59.4 16.1 5.5 0 1.8 5.5 11.7
7 59.4 14.1 5.5 0 1.8 5.5 13.7
8 59.4 12.1 5.5 0 1.8 5.5 15.7
9 61.4 10.1 5.5 0 1.8 5.5 15.7
10 63.4 8.1 5.5 0 1.8 5.5 15.7
11 65.4 6.1 5.5 0 1.8 5.5 15.7
12 67.4 4.1 5.5 0 1.8 5.5 15.7
13 69.4 2.1 5.5 0 1.8 5.5 15.7
Chemical analysis of body is given in table 1. Frit No. 2 when
applied on the body it showed crazing after maturing due to
excess amount of Na2O obtained from borax and sodium
carbonate. Similarly frit No.3 to 9, showed crazing. The
coefficients of thermal expansions of these frits from No.2 to 9
are more than the body. Although the number of lines of
crazing showed that crazing was gradually reduced as the B2O3
contents gradually increased while Na2O gradually reduced.
This is shown more clearly in table 3. Frit No.10 is free from
crazing and other defects. It also has the required maturing
temperature i.e. 960 °C. When 5 % clay is added with this frit
during frit during grinding and applied on the body, it matured
at temperature 1050 °C which is up to requirement because
most of the bodies are of low temperature. Above 1100 °C
they showed deformation. For such bodies, the frit maturing
temperature should not be more than 1050 °C. Frit No.11 is
also free from crazing but frit took more time to melt and it is
more viscous than No.10. Its maturing temperature is also high
i.e. 982 °C. Frit No.12 was melted at high temperature more
than 1550 °C.
It was highly viscous and difficult to flow. Its maturing
temperature was also high. Frit No.13 was melted at very high
temperature i.e. above 1600 °C. After melting it could not be
poured out due to high viscosity. Its maturing temperature was
also very high. So frits from No.11 to 13 are not up to
requirements. As frit No.10 is best composition so its thermal
expansion was determined on dilatometer i.e. Results revealed
that B2O3 is best replacement for PbO. It acts as a powerful
flux and helps to produce a smooth, brilliant covering within
limits. It also improves resistance to crazing to avoid
increasing the solubility of the lead. It also increases the
thermal shock resistance and reduces the surface tension. Boric
oxide proved a strong solvent action on the body and brought a
better interaction between body and glaze which reduced
crazing. Adding 12 ‒ 16 % B2O3 to a glaze composition
reduced it thermal expansion coefficient but further addition
causes it to increase.
3.1.Crazing test
The specimens were tested by dipping in the ink solution
for overnight and then the test pieces were observed visually
for crazing.
3.2.Autoclave test
The pieces were tested in an autoclave at a pressure of 50
Ibs/ sq.in. For two hours and then the test pieces were
observed for crazing.
Table 2. Analysis of the raw materials used
Sr.
No.
Name of raw
material
SiO2
%
Al2O3
%
Fe2O3
%
CaO
%
MgO
%
1 Quartz 97.40 1.86 0.35 0.85 0.15
2 Feldspar 64.60 22.08 0.42 2.80 ‒
3 China clay 44.03 40.61 0.71 0.75 ‒
4 KD pottery clay 41.80 38.55 0.45 2.80 1.26
5 Soap stone 62.35 0.17 0.05 ‒ 32.10
Fig.1. Chemical composition of 1‒13 formulations of frit

4. M. Saadet Khan et al. / Journal of Chemistry and Materials Research 1 (2014) 108–111 111
Table 3. Results of different frits after maturing based on autoclave test
S# Maturing Temperature
°C
Remarks
1 808 Soft glaze, low viscosity, free from crazing, high gloss free from all kinds of defects
2 822 Soft but less than No. 1, good gloss, crazed.
3 836 Less soft than No.2, good gloss, crazed.
4 850 Less soft than No.3 good gloss, crazed.
5 868 Less soft than No.4 good gloss, crazed.
6 886 Less soft than No.5 good gloss, crazed.
7 904 Less soft than No.6 good gloss, crazed.
8 922 Less soft than No.7 good gloss, crazed.
9 940 Less soft than No.8 good gloss, crazed.
10 960 Less soft than No. 9 good gloss, free from crazing, smooth surface, flawless.
11 982 Harder than No. 10 good gloss, free from crazing, but more viscous
12 1015 Harder than No. 11 good gloss, free from crazing, but more viscous than No. 11
13 1040 Harder than No. 12 good gloss, free from crazing, but highly viscous and not flow able.
Fig. 2. Maturing temperature of all 1‒13 compositions Fig. 3. Relation between composition and maturing temperature
4. CONCLUSION
The best to solve the problem of lead poisoning is the
substitution of B2O3 against PbO. Low temperature frits are
successfully developed with B2O3. Glazes containing B2O3 are
free from crazing; impart good gloss, low thermal expansion
coefficient, high mechanical strength and good acid resistance.
Borate frits during melting causes less corrosion than PbO
frits. The frit developed with B2O3 is more economical and has
all the prospects for industrial exploitation.
Acknowledgement
Authors offer their profound thanks to the Director Genral
PCSIR, Dr. Shahzad Alam and Dr. Sakhawat Ali Director
P&D for providing all necessary laboratory facilities. The
technical assistance is provided by M. Ameen,M. Boota,M.
sulaman Mr. Maqbool and Asif Ghani is also greatly
acknowledged.
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