Wadding
There are many wadding recipes floating around, so we decided to bring some together, and start doing some tests on them.
So far we have excluded high aluminium oxide recipes, partly because they are relatively expensive to mix up, and partly because they can leave a white mark on the clay, which I don’t find attractive.
Requirements
- Firm enough to support the pot, and able to stick to it
- Not welded to the pot by running glazes or flying ash
- Easily removed
- Neutral or attractive marks on the pot after the firing
- Moderate cost
Wadding Components
Wadding has the following major components:
- Aluminium based – the standard for soda and salt firing, but expensive and leaves white marks.
- Calcium – based on the traditional use of sea shells. The calcium carbonate in the shells is refractory, and calcium carbonate -> CaO with heat. Then it absorbs water when cold and should crumble away as it absorbs moisture after the firing
- Fireclay – highly refractory, acts as a resist, and also binds the wadding together to improve its wet properties
- Sand or grog – refractory materials, though don’t act as a resist or bind the wadding together
- Combustibles – sawdust, coffee grounds, flour…, all burn away early in the firing, leaving a porous wadding. The idea is that this then crumbles away easily, but it can also soak up ash or glaze, in which case the wadding is welded to the pot
Mixing
- Water – the handling properties of wadding seem to be very sensitive to the amount of water added, if anything being less tolerant than clay. Too much water, and the wadding won’t take any weight; too little and it crumbles.
- Maturing – wadding seems to improve with age, presumably the clay, sawdust etc all soaking up more water
Recipes
Note that all quantities are assumed to be by dry volume unless stated otherwise.Te comparison table at the end gives a quick comparison of the component types in each wadding.
Scallop Shells
Large and strong, ideal for big pots, but may need some wadding under them to make them sit better. Generally come off easily, unless they bond in with a glaze or lots of ash in which case they need grinding off, but leave attractive marks.
Cockle Shells
Similar to scallops but much smaller and weaker – need stuffing with clay to avoid a risk of collapsing. Good for small bowls etc, putting 3 round the foot
Kirk Mangus Fireclay Wadding
1 part each of silica sand, grog, sawdust and fireclay. No residue, leaves bare clay colour.
Tim Copsey recipe through Deniol Williams
1 part each of silica sand, sawdust and fireclay. See above.
Jean Sampson Salt Glaze Wadding
8 Alumina (either oxide or hydrated)
2 China clay
1 TWVD ball clay (or any dark or local)
1 Grog
Knead wheat flour into the mix to give a sticky consistency.
Used in the March 2020 firing for all wadding. It crumbles away very easily if it doesn't get saturated with running glazes or molten ash. Left white marks on some of the pots. Good for use on shelves and props, but not my favourite for pots.
Ben Brierley Recipes
A
2 silica sand
2 fireclay
2 kaolin
1 sawdust
Used in tunnel and lower back shelves in autumn 2019 firing. Holds shape well and also sticks well to the pots, so doesn’t tend to fall off when positioning the pots. Came off easily. No marks under the wadding, though may have caused some orange flashing around it on a low iron clay.
B
2 grog
2 fireclay
2 sawdust
Used in top back shelves in autumn 2019 firing. Not quite as good at holding shape or sticking to pots as A. Came off easily generally, but took a piece of pot off with it on at least 1 pot.
C
3 grog
3 fireclay
0.5 AT ball clay
0.5 red clay
3 sawdust
Recipes with ball clay or red clay leave a more attractive mark due to the iron, and come off very easily, more than if just fireclay. Possibly because the red clay softens early in the firing, making the wadding less porous and so less affected by absorbing glaze or wood ash.
D
1 alumina
1.5 silica sand
2.5 fireclay
1 sawdust
E
2 alumina
1 molochite 30 mesh
1 kaolin
1 sawdust
F
2 silica sand
1 fireclay
1.5 sawdust
His standard recipe, works well unless it gets saturated with ash.
G
1 alumina
2 silica sand
? fireclay
0.5 red clay
1.5 sawdust
Used in top shelves in autumn 2019 firing. Not quite as good at holding shape or sticking to pots as A or B. Came off easily.
Wobage
1 silica sand
1 fireclay
2 stoneware clay
4 sawdust
Very high sawdust. Used in middle back shelves in autumn 2019 firing, and under props and bottom shelves in front. Doesn’t hold shape, quite crumbly and pieces can break off and fall into pots. Comes off easily (though no glaze runs there) but doesn’t keep its shape under load. No visible marks. Best under bottom kiln shelves or on props as a wadding pancake.
Sargent
9 silica sand
1 fireclay
1 sawdust
Something wrong, doesn’t stick together. Possible transcription error, should be 1 of sand? Then same as Tim Copsey recipe above. Could only make it work by adding lots more clay.
Rose
1 silica sand
1 fireclay
Comparison Table
This gives a quick comparison. It doesn't differentiate between similar components, e.g. all clays are grouped together. Values have been normalised to add up to 10.
| Recipe | Al | Ca | Clay | Sand/grog | Combustible |
| Shells | 0 | 10 | 0 | 0 | 0 |
| K Mangus | 0 | 0 | 2.5 | 5 | 2.5 |
| T Copsey | 0 | 0 | 3.3 | 3.3 | 3.3 |
| J Sampson | 6.2 | 0 | 2.3 | 0.8 | >0.8 |
| BB A | 0 | 0 | 5.7 | 2.9 | 1.4 |
| BB B | 0 | 0 | 3.3 | 3.3 | 3.3 |
| BB C | 0 | 0 | 4 | 3 | 3 |
| BB D | 1.7 | 0 | 4.2 | 2.5 | 1.7 |
| BB E | 4 | 0 | 2 | 2 | 2 |
| BB F | 0 | 0 | 2.2 | 4.4 | 3.3 |
| BB G | 1.8 | 0 | >1.8 | 3.6 | 2.7 |
| Wobage | 0 | 0 | 3.8 | 1.2 | 5 |
| Sargent | 0 | 0 | 0.9 | 8.2 | 0.9 |
| Rose | 0 | 0 | 5 | 5 | 0 |
Information Sources
Active Wadding – Ben Brierley (and recipes link) http://www.ben-brierley-woodfired-ceramics.co.uk/Active_wadding_article.html
Wadding for Wood Firing by Simon Levin http://glinca.si/wp-content/uploads/2017/11/Ceramic-Arts-Daily_WoodKilnFiring.pdf
Wood Fired Ceramics by Coll Minogue and Robert Sanderson