Hollowing-out

It’s the last day. Two students are continuing to model Dave, while the other five are going to hollow-out the clay head so that it can be fired. Everyone has hollowed out at least one head before, if not many more. Normally you would leave the clay to become ‘leather-hard’. But as we need to do it on the fifth day of the course the clay will always be a little too soft. Experience shows that we will need the afternoon to do a bit of remodeling. We run through the principles of hollowing-out ie why we do it rather than just putting the portraits straight into a kiln. A successful firing of a sculpture is ultimately about having an even thickness of clay throughout the sculpture and carefully managing the drying process. A thick section of clay next to a thinner section of clay means that the thinner will dry more quickly and lead to cracking. It also helps if we avoid getting air bubbles in our sculpture as we put on clay – moisture trapped in air bubbles can lead to the sculpture exploding/shattering in the kiln. In order to get an even thickness we need to scoop out the ‘brains’ of the portrait. Just a warning – the following explanation may only make sense to those who have had a go at this process or are familiar with clay!

First, we cut off a ‘skull cap’ shape from the top/back of the head. We use a wire cutter (like cheese-wire) to do this. Before we lift the skull-cap off, it’s good to make some marks so you can line-up the skull-cap correctly at the end of the process. We lift off the cap and put it somewhere safe (and not in the sun as we don’t want it to be drying out). We  then dig out the clay from inside this ‘skull cap’ and from inside the main head (see photo). We use ‘hollowing-out’ tools – these are basically hoops of stiff wire attached to handles. You need to take care to feel the thickness of the remaining clay as you scoop out. It’s all too easy to get over-excited and dig through the side of the neck! Mind you, you can always add some clay to the inside of the neck if you do. I am aim for around 3.5cm thickness. But it won’t be possible to get it that thickness everywhere (for example, the neck).

Scooping out the 'brains'

While we are doing this we leave the sculpture on the armature for as long as we can. It means it is nice and stable and we are avoiding ‘squidging’ the clay. Because the wooden bust-peg will start to get in the way, we need to get the portrait off the armature. We can then dig some more clay out from the top, before we then dig up into the neck from the bottom. It is at this stage that we also decide whether we want to chop off any extra clay that we have at the base of our portrait. If you do, then make a cut with a wire cutter at this stage.

Getting the head off the post is easier said than done. We place them on the floor and literally stand on the wooden base, standing over the sculpture. We have the nose facing away from us, and we clasp the portrait under the chin and at the back of the neck (or under the shoulders at the back) – then ease the sculpture straight up and off the armature. On day one we covered the wooden post with newspaper, so this helps it come off smoothly. At this point you need to have already laid everything out you need. A chair nearby, an old pillow, a bin bag for the clay bits you will be removing, and your hollowing out tools. It does help to have other people around as the clay sculpture is pretty heavy and hard to move once off the armature. Once you have it on your lap – sitting upright with the nose away from you – you can dig out some more clay, carefully. Widening the hole that runs through the neck is quite important.  We’ll come back to that.

Once you have done all you need from the top, turn the sculpture over, on your lap, so it is resting on where the ‘skull-cap’ was removed. You can now hollow-out from the bottom. But careful – the sculpture needs to be able to stand while it is drying out and will be quite heavy, so don’t go mad. But if you dig out too much from the shoulders, you can always add clay back in. Or you can create a thick clay supporting wall under the shoulders (this last statement will probably make no sense at all unless you have tried this before!).

In order to replace the ‘skull-cap’ of clay on the top of the portrait, you need to have the sculpture standing upright. I prefer to dry my portraits out on a stand as it makes them more stable. This is particularly important if you need to transport the sculptures (now or later, like the students will) or the model’s pose/posture means that the weight of clay may pull the sculpture over. Dave’s head is held quite far forward in comparison to his shoulders, so not having their sculptures back on a stand will be problematic. Also, if you prefer not to have a flat bottom to your sculpture, it will not be free-standing so needs the support of a stand.

Having said all this, if you pop your sculpture back on the same armature as you sculpted it on, there are a couple of danger points to be aware of relating to how clay shrinks when drying. How to explain this? If the top of the wooden post is too close to the replaced clay skull cap, as the sculpture dries the whole weight of the portrait may literally end up hanging from the top of the armature post.  Why? The wooden armature is going nowhere. So if the clay shrinks, and the top of the sculpture is very close to the top of the wooden post, then the shrinking will be noticeable at the base of the sculpture (ie the sculpture is having to shrink upwards).  This is when the top of the head might pop off! Also, if you have not, or have not been able to, hollow-out the neck enough problems may occur. The shrinking of the clay as it dries means that the clay could shrink onto/against the wooden post. Again, the post is not going to give, the clay will. And it might crack. For this reason I normally have a range of armatures to hand that have shorter and thinner posts.

So – the sculpture is now placed on an appropriately sized armature. We now need to re-attach the skull-cap of clay. We need to have some ‘slip’ to hand (watery clay). You need an empty glass jar, to which you add small bits of clay and a little water. With a fork, or similar, you need to mix this until it is the “consistency of double-cream”, as my old tutor used to say. To prepare the surfaces you are joining, you need to scuff the clay up a little. Use a blunt knife or a modeling tool to make criss-cross small cuts in the clay. You then gently apply slip to both the parts you are joining – a paintbrush or a knife will do. Just don’t flatten all those nice divots you have made in the clay surface. You then replace the skull-cap (the right way round!) and gently push into place. You can mop up any excess slip that oozes out. The important thing is to then ‘unite’ the two sections. Get a small wooden modeling tool and push clay from above the join to below, all-round. You will therefore end up with scores across the join, up 1 to 2 centimetres. This is helping to make the join permanent, mixing the clay from above with that below. You can now re-model around the join and rectify anything else that has got a little damaged in the process (eg ears can easily get a little squashed). Today the students have the whole afternoon to carry on working with Dave.

Once you have completed the last tweaks you need to manage the drying process. In order to dry the sculpture safely, you need to dry it out over a period of up to eight weeks. Inevitably there will still be thicker and thinner sections of the clay, so the slower you dry it out the better, to avoid cracking. For the first week I would leave it wrapped in a black bin liner (away from sun and radiators). The second week I might loosen the bin liner so some air can get in. Week three I might remove the bin liner and cover the sculpture with lots of sheets from a ‘broadsheet’ newspaper. It looks a bit like you have made it a nest. A week or two later I might leave it with just 3 or 4 sheets of newspaper covering it. After that I would remove any covering. Then I might move it into a warmer room or nearer to a radiator. You will know it is dry when the whole sculpture has changed to a lighter colour. It is then ready to take to the kiln. I use the South Heighton pottery where Chris is incredibly experienced at slowly firing sculptures. It takes three days. One day the kiln is getting up to temperature, it is then firing for one day at the highest temperature, then takes a day to cool down. Then you are ready to colour or patinate the sculpture.

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4 thoughts on “Hollowing-out

  1. This is very helpful thank you. I have an additional question if you don’t mind. I don’t have access to a kiln at the moment, so I may have to leave my portrait drying for even longer than you would suggest. I understand there is a minimum, but is there also a maximum drying period?

    1. No maximum drying time if you have hollowed it out. Usual precaution – if you are standing it on an armature/bust-peg whilst it dries, make sure the peg is not too tall or thick during the drying process, as shrinkage will occur as the clay dries (and if the clay shrinks against the post at the sides or top, cracking is likely to occur). Good luck!

  2. I have a question, in regards to firing the sculpture after it’s dried. Is there a certain formula for firing portraits? I

    1. Hi Camisha – I always take my portraits to a kiln/pottery where they are used to firing sculptures (as opposed to ceramics). I know that’s not very helpful! The rule is to fire the sculpture over three days – slowly up to temperature, keep at temperature, then slowly down. Each bag of clay you use will give the firing temperature. The Clayman website is helpful – for example, the clay I tend to use is Swan Blend, and on their website they give the properties of the clay and the firing temperature range – https://www.claymansupplies.co.uk/cms/cms.jsp?menu_id=17804&prodref=1000%2F12.5&proddesc=SWAN-BLEND&category=CLAYS+-+RED&catdesc=Red-Coloured
      Hope this helps!
      Hazel
      : )

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