CTM Potters Supplies - if you use clay you need CTM

Doncaster  Tel : 01709 770801

Simba Materials Limited t/a

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Exeter  Tel : 01395 233077

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admin@ctmpotterssupplies.co.uk CTM Potters Supplies - Exeter, Unit 10A Mill Park Industrial Estate, White Cross Road, Woodbury Salterton EX5 1EL



16  Antimony Trioxide

Sb2O3     Additions of 1-2% to a lead glaze gives a yellow - often known as Naples Yellow. Toxic.

17  Chromium Oxide

Cr2O3     Usually 1-3% produces greens but will give pink in the presence of tin; can produce reds and yellows in a low firing lead glaze (if no or very low alumina), and browns in zinc glazes. 1% in a lead/soda glaze gives a yellow.

11  Cobalt Carbonate

1  Cobalt Oxide

The carbonate has a lower cobalt content but is easier to mix evenly and melts easier. 1-3% carbonate or 0.8-1.5% oxide produces deep blues in leadless glazes, or a blue-black in lead glazes, or a vivid blue in alkaline glazes. The presence of magnesium gives a more purple tint.

12 Copper Carbonate

15  Black Cupric Copper Oxide

83  Red Cuprous Copper Oxide

A strong flux that can cause the solubility of lead in low-sol glazes. The carbonate is weaker but is easier to mix reducing the risk of speckle. 3-7% in the carbonate, or up to 5% in the oxides, will give an apple green colour under both oxidising and neutral conditions; yellow-greens in a potash glaze; blue-greens in a barium glaze; turquoise blue in an alkaline glaze. High lime glazes can create purples; high lime glazes with alumina can create purple sploges. Fired under reduction in an alkali glaze (with addition of tin) it creates a copper red or sang de-boeuf. Some prefer to use the cuprous copper oxide when making reds.

31 Illmenite coarse

32  Illmenite fine

An iron ore with significant levels of titanium, most often used in coarse / granular form to produce dark specks in clay or glaze. Fine grades produce tans and buffs. Has a higher iron content than rutile.

18  Iron Oxide, Red Ochre

2-10% red will achieve colours from honey to dark brown. Depending upon the firing conditions brownish reds, brown, black, yellow and even purple can be produced. Reducing conditions create a blue colour. 0.1% titanium dioxide can help stabilise yellow/orange colours.

66  Iron Oxide, Black

4-8% black oxide will produce brown to black in normal conditions and crystals in aventurine glazes.

73  Iron Oxide, Yellow Ochre

3-8% gives yellow to brown colours. The weakest but most miscible of the iron oxides. A good painting pigment.

70  Iron Spangles

Gives black and brown speckle effects.

19 Manganese Carbonate

20  Manganese Dioxide

0.2% to 5% creates brown colours in glazes; pink, purple or plum colours in alkaline glazes. when mixed with iron it produces brown. When mixed with cobalt it produces violets. It helps create a black with iron and cobalt together. It is a strong oxidising agent.

21  Nickel Oxide

1-3% gives dull browns, greens or greys but used to modify other colours wush as creating a moss green with chromium, or a red violet with manganese in a soda glaze. a loight violet in a lead or high potash glaze. In high zinc stoneware glazes it can produce yellow in oxidation or blue when reduced.

33 Rutile

A natural ore containing titanium dioxide with lower levels of iron than  the illmenite ore: used to produce ivory to mottled brown colour in oxidation, purples and blues under reduction - especially in combination with a trace of illmenite. Excellent for modifying other stains or oxides and creating mottled or streaked effects.

59  Silicon Carbide

Highly refractory material used to create bubbles; though in highly alkaline glazes 1% can create a copper red style colour.

25 Tin (Stannic) Oxide

4-7% will produce a semi-opaque glaze, white (with a blue hint) at 5-9%, 8-10% will give a full opaque. Useful as a white decorative pigment / underglaze - either alone or mixed with a small amount of a transparent glaze. Copper red glazes need tin, chrome and tin produce pinks if no zinc or boron is present. If any chrome glazes are fired in the kiln it can turn a tin white glaze pink. Tin and iron can create variegated surfaces.

26  Titanium Dioxide

Up to 10% will produce a creamy white finish with a matt or semi-matt surface. 0.1% titanium dioxide added to an iron glaze can help it to stabilise in the yellow/orange spectrum. High fired matt iron oxide and titanium glaze s can produce red colours. Below 1% it can increase durability; above 2% it creates minute crystals softening colours - increase in level will create variegation in the surface eventually creating matt surfaces.

22  Vanadium Pentoxide

Up to 10% will give a weak yellow, stronger in conjunction with tin. Can be used at higher temperatures than antimony trioxide

27  Zinc Oxide

Reduces expansion, improves craze resistance, gloss, whiteness, durability, and in low alumina glazes promotes crystal growth. Presence of zinc in glazes can affect colour production of other oxides - not recommended with copper, iron or chrome.

29  Zirconium Silicate  Zirc 5

Extremely stable, surviving without melting at very high temperatures. 4-7% produces semi opaque, 8-10% usually produces full opacity but some transparent glazes do require more. Has a low expansion so tends to reduce crazing but crawling and pin holing can occur in high zircon melts - normally solved by cooling clower and ensuring a good bond when applying the glaze. Reacts less with colourants in the glaze than tin does - significantly cheaper than tin but only half as effective. Zircon stiffens the glaze and produces a harder glaze surface and reduces thermal expansion more than tin.

It is incredible how the combination of different formers, fluxes and oxides can produce a myriad of colours - often not producing what you expect until you check every ingredient in the glaze and the way it interacts. Keep a note of all the odd events - you might wish to replicate it only you could remember how!

Metal Oxides Raw Materials

56  Calcined Alumina

Al2O3  Fine white granular powder increasing glaze viscosity, firing range and resistance to crystallisation. Very high melting temperature. 15%+ in a glaze can impart matt and opaque effects - best introduced from kaolin or frits. Also, used in Batt Wash.

57  Hydrated Alumina

Al2O3.3H2O  As "Calcined" but stays in glaze suspension better. Can help with removing of finely dispersed bubbles in glazes. Can enhance Cr-Al pinks.

HP71  Ball Clay, Hyplas 71

20% Al2O3, 70% SiO2, 0.8% Fe2O3, 2.3% K/Na2O3  A high siliceous Devon ball clay giving good plasticity with medium strength and useful low iron content. Ball clays are very plastic and fuse relatively easily with greater density than china clay - usually used along with china clay due to high shrinkage levels.

23  Barium Carbonate

BaCO3  Used in casting slips at low levels to prevent scumming (up to 0.5%). Used in high temperature glazes as a flux, and produces matt/semi-matt surfaces at earthenware temperatures. At higher temperatures it can make a distinctive turquoise with copper. In bodies it can give higher translucency but lead to increased weakness and excessive shrinkage

BW  Batt Wash

A mixture of aluminas and china clays to be scattered as a powder or used with water to make a paste.

44  Bentonite

Al2O.2H2O.SiO2  Most plastic and impermeable common clay materials. It binds particles together making bodies stronger in the green and dry state. Its' minute particles fill voids between others to produce a more dense mass. Adding bentonite to glazes imparts better dry strength and a harder more durable surface. 1 part bentonite can plasticize 10 parts of kaolin. Bentonite bodies are stronger but dry slower, crack more and fire darker with potential iron specks. 1-2% bentonite added to the dry powder can greatly improve glaze suspension. Bentonite containing clay bodies may look dry but may not be - they must be very slowly dried to prevent steam being produced and creating cracks. Make into a paste before adding to glaze batches if not added dry to the powder.  

64  Bone Ash

Ca3(PO4)2  Can be added to porcelain to make bone china - bone china is non-plastic, unstable in the kiln and difficult to fire consistenlty due to a very narrow firing range. Up to 2% bone ash can be used in enamles for opacification - more will create pinholes. Too long a firing or too high a temperature will result in blisters. Not suitable for slip casting.

45  China Clay, Puraflo

Al2O3.2SiO2.2H2O  General purpose kaolin. Much larger particle size than ball clay or bentonite so often used together to make a good cross section of particle sizes imparting enhanced working properties. Kaolin speeds up casting rates in slurry bodies and drying rates in all bodies. Low plasticity and so is usually used (up to 50%) in combination with ball clays and other plasticizers. It is the most common glaze suspender.

104  China Clay, Grolleg

Grolleg china clay is a little lower in iron and higher in potassium making it a whiter stronger material particularly suitable for casting.

77  Colemanite

B2O3 43.9%, CaO 26%, SiO2 4.5%.  Insoluble source of boron. A powerful flux which can intensify colouring oxides and increase craze resistance - however make sure that you sieve out any coarse material.

46  Cornish Stone

K2O 3.8%, Na2O 4%, Al2O3 15.3%, SiO2 69.5% typical.  Secondary flux in earthenware glazes, and an alternative to feldspar at higher temperatures, giving greater fired strength. Low iron and high silica content promotes whiteness and transparency so particularly useful in porcelain and white bodies.

47 Dolomite

CaO3 31.4%, MgO 20.8%  Used as a source of magnesia and calcia to act as a secondary flux. A principle source of MgO in high temperature raw glazes (though can be used at 1060oC) and above 5% will opacify, making a matt glaze at higher levels.

48  Feldspar, Finish Flotation

K2O 7.5%, Na2O 3.2%, Al2O3 18.5%, SiO2 67.5%  A halfway product between Soda and Potash Feldspars making it a more stable product at mid temperatures.

49  Feldspar, Potash

K2O 11.3%, Na2O 3.2%, Al2O3 18.5%, SiO2 65.8% typical    For medium and high temperature glazes - if a recipe lists feldspar or felspar it probably means Potash Feldspar. If trying to identify some it is not as white as soda. Glazes with 35%+ feldspar are likely to produce crazing problems, more than 50% will be unbalanced and probably lack adquate glassy formers in the glaze.

50  Feldspar, Soda

K2O 2.8%, Na2O 8.5%, Al2O3 18.5%, SiO2 69.5% typical  More suitable feldspar for lower temperature glazes.

51  Flint

SiO2  Major source of calicned silica for glazes and clay bodies (15%). Increases the fired temperautres and craze resistance of glazes and helps stabilize glazes due to its low expansion and contraction - reduces shrinkage and crazing.  US recipes may state quartz when  they mean flint.

2  Gillespie Borate

2CaO.3B2O3.5H2O  Brand name of a useful naturally occurring colemanite, (unlike a well known no longer available similar named material) this is carefully blended to give a reliable fluxing action. Often used in Raku recipes.

24  Lithium Carbonate

Li2CO3  A very strong flux, used to reduce viscosity, reducing maturing times and lowers firing temperatures without affecting the firing range. 1% can increase gloss to a marked degree, 3% can reduce melting temperatures by several cones. However, more than 5% can cause devitrification, shiver and pin holing. Increases colour response of copper and manganeses. Can create mottled effets due to flow.

58  Magnesium Carbonate

MgCO3  Produces matt / velvet finishes above 1200oC (for lower temperatures see the less pure Dolomite) and in reduction; at lower temperatures it can produce matt finishes when used at high levels. Promotes pastel or earthy shades of colours in high temperatures. A flux at high temperatures.

52  Nephylene Syenite

K2O 9.1%, Na2O 7%, Al2O3 24.9%, SiO2 56%  More fusible than feldspar, it has lower silica and higher soda and potassium levels and so can be used a lower melting temperatures. Important for use in vitreous bodies.

68  Petalite

K2O 0-2%, Na2O 1.6%, Li2O 4%, Al2O3 15.7%, SiO2 76.1%  Natural lithium bearing material used a flux in earthenware and stoneware. Lowers maturing temperatures without shortening firing range and increases resistance to thermal shock. At high temperatures it reduces crazing. Increases colour response of copper and manganese.

53  Quartz 300

C600 Quartz 600

siO2  Powdered quartz is used in glazes and bodies to give strength. Very fine grades such as the Quartz 600 can be used as a carrier for underglazes and stains or act as fillers in bodies; generally recommended for glazes is the Quartz 300. however, if using quartz there should be sufficient fluxes to prevent conversion to cristobalite during firing.

69  Sodium Carbonate

Na2CO3  Sodium Carbonate some times referred to as Soda Ash is often used along with sodium silicate to produce slips that do not gel too quickly and stay wet longer. sodium Carbonate is the preferred deflocculant for thinning glaze slurries. Ideal flux for Egyptian paste glazes.

106  Spodumene

Li2O.Al2O3.4SiO2  An active flux used in small amounts in glazes. Can help reduce thermal shock in bodies. Lithium bearing natural material similar to petalite reducing maturity times and lowering firing temperatures and increasing gloss.

40 Strontium Carbonate

SrCO3  Flux used above 1090oC with similar effects to whiting and zinc oxide but with less pinholing, and can be used as an alternative to lead as it increases gloss and gives good heat shock resisistance - though excessive amounts will give a crystalline matt surface.

54  Talc

MgO 32/33%, SiO2 46%, CaO up to 8%, Al2O3 up to 9% typical  Important source of MgO flux for bodies and glazes. Talc has a less high loss on ignition than dolomite or magnesium carbonate and so produces less glaze bubbles, blisters and pinholes. High temperature magnesia matt glazes often use talc and magnesium carbonate together to form magnesium silicate crystals on cooling to give opacity and a silky surface. Reduces plasticity in bodies and so is more suitable for castware. Used to produce thermal shock resistant / flameproof stoneware bodies where it acts as a low expansion flux converting quartz in clays to magnesium silicates. In amounts up to 5% it can improve maturity and melting. Mix into a paste before adding to glaze batches.

55  Whiting

CaCO3  Fine calcium carbonate / limestone used as the principle source of lime in glazes. It acts as a flux at high temperatures. Enables thicker calt glazes. Too much whiting leads to dull and rough surfacess.

67  Wollastonite

CaO.SiO2  In low fired ceramics it reduces drying and firing shrinkage and warpage. It promotes lower moisture and thermal expansion in firing. Valuable component of tile bodies as it releases no gasses and helps other gasses vent out early. Stronger flux over 1100oC. Wollastonite is a useful alternative to whiting when pinholing is a problem and where talc would introduce too much MgO. Often used to supply CaO in a more easily melted form in stain and frit formulations.

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87  Silica Sand 60

SiO2  A medium silica sand (can be used for placing) mainly used as a grog, making the body more refractory adding strength. We sometimes have other silica grog sizes in stock.

82  Molochite 30/80's

100  Molochite 120's

72  Molochite 200's

Al2O3 37%, SiO2 48%  White calcined china clay used as a fine powder to increase the firing temperature and reduce the tendency to crawl of glazes that have high clay content. Larger sizes are used as grog inducing mechanical stability and resistance to thermal shock through the development of mullite crystals.

107 Corderite 30's to dust

108 Corderite 16/30's

Calcined Ball and Fire Clays - similar to Molochite in use but darker grains - it is often used to add strength to larger pieces and is often used in wood firing and raku clays.



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PP1  Potters Plaster

General purpose potters plaster - also known as Plaster of Paris

89  Dental Plaster

Used for working moulds with fine details, also for modelling

91  HP2 Potters Plaster

Harder than potters plaster, for batts, moulds and modelling

Typical ratio of plaster to water to make a mould:-

Cast Moulds for China Clays           1.25 kg plaster to 1 litre of water

Cast Moulds for other clays            1.35 kg plaster to 1 litre of water

Handpressed Moulds                     1.40 kg plaster to 1 litre of water


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37  Calcium Borate Frit

1030 - 1180oC  6.9 Expansion  SiO2 17.9%, B2O3 50.3%, MgO 0.1%, Al2O3 4.9%, K2O 0.3%, CaO 26.5%  For use where recipes specify greater than 5% colemanite. Can be used as a base in lead free glazes.

71  Ferro Frit 3110

950-1050oC  10.1 Expansion  SiO2 69.8%, Al2O3 3.7%, B2O3 2.6%, K2O 2.3%, Na2O3 15.3%, CaO 6.3%  Soft low alumina sodium borosilicate frit for glazes. Often used in crystal and crackle glazes. Helps in the production of copper blues and manganese purples, and raku glazes. High expansion frit.

xx  Ferro Frit 3124

1000-1150oC  7.9 Expansion  SiO2 55.3%, Al2O3 9.9%, B2O3 13.7%, K2O 0.7%, Na2O3 6.3%, CaO 14.1%  Often added to glazes to make them melt at lower temperatures - it is a quite balanced glaze frit, increasing the boron content without odervly disrupting the balance of other oxides.

xx  Ferro Frit 3134

1000-1150oC  9.6 Expansion  SiO2 46.5%, B2O3 23.1%, Na2O3 10.3%, CaO 20.1%  Similar to 3124 but higher in boron and calcium with no alumina. The low alumina is useful as it allows you to use more clay in a glaze. It can be added to a glaze without having to reduce the clay content.

35  High Alkaline Frit

860-1060oC  SiO2 52.5%, B2O3 3.4%, Al2O3 5.2%, Na2O3 18.6%, K2O 10.3%, CaO 2.9%   A high alkaline (soda and potash) version of a borax frit. High expansion rate making them suitable for crackle glazes. Helps create turquoise copper blues and purple/brown manganese in glazes.

34  Lead Bisilicate Frit

900-1100oC  SiO2 29%, Al2O3 12%, PbO 59%  Good clear, general purpose lead frit for developing rich, bright surfaces and good reaction to colours. Safer way to introduce lead than lead oxide, particularly suitable for red clays.

41  Lead Sesquisilicate Frit

860-1080oC  As above but specially coated to reduce solubility.

36  Standard Borax Frit

960-1120oC  SiO2 49.9%, Al2O3 7.5%, B2O3 18%, CaO/MgO 14.1%, K2O/Na2O3 10.5%  Often used in the production of earthenware glazes when a lead-free glaze is required. a slight milkiness, especially at low temperatures, may be evident over red clays, and the colour response with oxides etc is not as vivid as with lead frits.



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WR  Wax Resist

A pre-mixed masking medium used to coat areas on which no glaze is required. Water based and so it can be affected by bacteria growth - a small drop of bleach will elimnate this problem. Will give off fumes during firing.

LR  Latex Resist

A natural occurring latex, works similar to wax but easier to peel and alter.

75  Sodium Dispex

A liquid electrolyte deflocculant to be added one drop at a time, stirred, wait, check - to make a slip more fluid - can also help mould life. A clip with too coarse a material will not deflocculate. Used to replace sodium silicate and sodium carbonate.

76  Sodium Silicate 75TW

76a  Sodium Silicate 140TW  

TW is for measuring specific gravity in degrees of Twaddle (named after William Twaddle) - beer is higher SG than water so someone with a lot of beer in them talks a lot of twaddle.

Sodium Silicate is a liquid electrolyte deflocculant to be added one drop at a time, stirred, wait, check - to make a slip more fluid.  The 75 TW is for bone china and porcelain.

Typical Casting Recipe for non-porcelain / non-bone china:

i) 10 kg plastic clay, 10-25 g of Sodium Silicate 140 TW, 10 g of Sodium Carbonate, 1200 cc of water.

ii) 10kg powdered clay, 12-30 g of Sodium Silicate 140 TW, 12 g of Sodium Carbonate, 4000 cc of water.

Tone  Bentone EW

A colloisdal powder flocculant. Adding 0.33% into a glaze powder will usually keep it in suspension - many add it to all their earthenware recipes as a preventative measure. More powerful than bentonite where up to 2% mixed in to the dry powder is used.

74  Calcium Chloride Flakes

Dissolve a small amount in hot water, then add to the glaze slop one drop at a time, stir wait, check - acts as a flocculant to make glaze more fluid - especially in earthenware pre-prepared glazes that are to be kept a while.

FS200  Fluxing Agent

Between 1% and 2% in underglazes or as an addition to glazes to make them more brushable.

GUMA  Gum Arabic

Used in water as a medium for underglazes or stains and in glazes as a binder.

SS  Soft Soap

Dilute with 3 parts water and apply with a brush - used to ease separation in moulds.

SCMC  Cellulose Glaze Binder

We recommend creating a 2% solution and use it as follows:- a) for brush on glazes use the 2% SCMC solution for 20-25% of the weight of the final brush on glaze; b) for dipping glazes use 2% SCMC solution for 5-6% of the weight of the final dipping glaze.