Weekend Projects - Sgraffito pot archive

Friday 17 June 2016

Andy Coates experiments with sgraffito on a turned pot

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By now you will no doubt have noticed that I enjoy playing with surface treatments on woodturning. This month’s project is no different. I am going to turn a simple pot/vase form and decorate it using a technique called sgraffito. Sgraffito is a form of decoration made by scratching through a surface to reveal a lower layer of a contrasting colour, it is more usually done on plaster or stucco on walls, or in slip on ceramics before firing, but is also used in fine art painting.

Using this technique on woodturning is not a new evolution; Al Stirt has been using the technique to glorious ends for quite some time. Al uses the wood as his substrate to be ‘scratched’ through to, whereas I will use a slightly different technique, closer to the way it might have been achieved historically. Either approach is fine, and you may decide to use one over the other.

Sgaffito has been used to great effect by many potters and ceramicists, and a similar process has also been used in fine glassware. Look around for examples to use as inspiration for your own work. Tim Christensen, an American potter who uses sgraffito on his porcelain forms uses the technique to stunning effect, and his work is well worth looking at. Try to use references like this as inspiration, rather than simply copying them; the real sense of fun and achievement is in developing your own style.

Rather than using the wood as the base coat, I prefer to apply gesso, as this provides a pleasing pure white relief. You could of course, simply colour the wood with acrylic and cut through the paint to the wood. The choice is yours. The beauty of the technique is that it provides an effective and striking contrast without being technically difficult; it is, after all, simply scratching away paint. Before anybody says ‘but I’m not artistic’ (again!), you don’t need to be. Look at it as doodling. You’ve all doodled. This is no different. You can start with simple repeated patterns and shapes, develop ideas and themes, or perhaps use the vessel as the canvas for a story told through sgraffito. For the purposes of this project I made mine as part of a series I had already begun. You might also use different colours for base and top coat. The options are wide open with this kind of decoration.

The base coat I am using is white gesso, which can be bought from any good art supplies company. There is a truism I’ve discovered in relation to art materials: you get what you pay for. Cheap gesso is not worth buying. Choose a good quality brand, and if you have an option opt for a medium-thick consistency. The same applies to the acrylic paints you choose. Cheaper brands use poorer quality pigments and they often disappoint. Choose good quality brands and the colour, hold, durability and light fastness will be significantly improved. One thing to keep in mind though is that we’ll be using these in a manner not described on the label. So we take a chance that the results are suitable. My experience indicates that the results are fine. So if you’re happy to stretch your creative muscles and take a risk, let’s get to it.

Tools used:

¾in spindle roughing gouge

½in long grind bowl gouge

3mm parting tool

6mm parting and beading tool

Forstner bit on extension bar

6mm carbide hollowing tool

Rolly Monroe mini hollowing tool

Little Sister hollowing tool

Various tools for ‘scratching’

End grain sycamore block (Acer pseudoplatanus) 200 x 200 x 100

White gesso

Black acrylic paint

Brushes

UV sealer

STEP 1

Mount the workpiece between centres and using a spindle roughing gouge, rough down to a true cylinder. Take care to work off the ends of the blank, reversing the direction of the cut when you get to the headstock end

STEP 2

Use a small parting and beading tool to cut a tenon to the size appropriate for your particular scroll chuck. Make the face surface slightly concave to provide a good seating in the chuck. Mount the blank on the chuck

STEP 3

Using a long-ground bowl gouge, or spindle gouge if you prefer, begin to put the shape in to the blank. As this is a decorative object the base can be smaller than for a utility piece, but remember you need some support for hollowing, so you may prefer to do the shaping in two stages, the second stage after hollowing out

STEP 4

To make the hollowing process easier, and to help prevent going too deep, it helps to bore out the slower turning wood at the centre. You can achieve this in a number of ways. A hand-held twist drill, an engineer’s twist drill on a Morse taper holder, or with a Forstner bit on an extension bar in a Jacobs chuck. Whichever method you choose, make sure you withdraw the drill frequently and remove the swarf to prevent binding

STEP 5

Mark the depth you wish to drill to on the bar, and here you will notice that I have also marked the internal depth on the outside of the form. I have also marked the diameter of the Forstner bit to provide a reference later if I decide to adjust the external shape later

STEP 6

With the lathe running at 400–500 RPM slowly drill down to depth, withdrawing at regular intervals to remove the swarf. Once this is done you are ready to hollow the form out

STEP 7

Usually I would hollow out with one tool, but here I chose to use a new tool, the Little Sister from Hamlet tools. To provide a comparison I also used two other hollowing tools

STEP 8

When using tipped hollowing tools ensure that the shaft of the tool is properly supported. This may require the toolrest to be sited further away than for a conventional gouge

STEP 9

With the cutter shield set to a medium cut, address the wood at about the eight o’clock point, and, using the cutter shield as a bevel, feather the cutting edge onto the wood. If you have not used this type of tool before you may need to practise this cut. You can adjust the depth of cut by gently rotating the tool one way or the other. It will cut equally well forwards or backwards

STEP 10

Once mastered, you will find it cuts easily and produces long streamers of shavings. Continue hollowing, aiming to keep the wall thickness even throughout. Set the thickness near the rim and then work down adjusting as you go. The cleaner the surface you leave the less work you will have to do later with scrapers or abrasives. During hollowing I used all three types of tool at various stages

STEP 11

When you get close to the bottom you may find the tool vibrates, which leads to chattering and a poor finished surface. Take finer cuts and make sure the tool is well supported on the rest. Once the hollowing is completed you may need to use a curved scraper to clean the surface. Abrading down a deep narrow vessel is best done on a bar with abrasive attached. Work through the grades as usual and then seal and wax the interior

STEP 12

Before we can begin decorating the vessel we need to finalise the exterior shape, and once this is done we also need to make a shallow parting cut to give us the base to work to. Abrade the surface to 240 grit and use a tack cloth to remove the dust

STEP 13

Clear the lathe of shavings and cover the lathe bed and any exposed electrical equipment with paper or a dust sheet. The white gesso is applied with a brush. Don’t apply it too thin, nor too thickly. For a more uniform surface you can run the lathe at its slowest speed and drag the brush slowly up the form. Be careful of spraying gesso!

STEP 14

You can either leave the gesso to cure, or speed up the drying time with a hair dryer or a heat gun. Don’t let the wood get too hot and take your time

STEP 15

At this stage you can gently abrade the surface to provide a smooth uniform base for the second coat. The dust produced is very fine so use a mask and dust extraction. Apply a further coat of gesso and repeat the Appropriate steps above. If you want to you can repeat this step one more time. This provides a good thick base coat

STEP 16

Once the last coat of gesso is cured and gently abraded we are ready to apply the colour. I use a good quality acrylic paint and decant some into a small pot to avoid mishaps

STEP 17

Cover the whole pot and try to keep the brush strokes even and flowing. You could rotate the lathe again at its slowest speed and use the brush to draw the paint along the form. The acrylic now needs to cure and dry. Once again, you may choose to speed up this process with gentle heat. Do not overheat the paint or it will bubble

STEP 18

Once dry we can begin to think about the sgraffito. I prefer to have areas delineated within which I can apply decoration. Here I am using a sharpened stick of hardwood to scratch lines in the paint. Rotate the form by hand and aim to only scratch through the black paint to reveal the pure white gesso beneath. Once my ‘frames’ are marked in I part the piece off the lathe

STEP 19

The sgraffito can be applied with any number of implements or tools, even the odd thing that isn’t a tool – if it will scratch it can be used. Here are a selection of things I regularly use. You will find additions to this list as you progress

STEP 20

For simple, geometric patterns I find a small ‘V’ carving tool works well and produces nice clean lines. Remember ... you are only aiming to cut through the paint, not into the wood

STEP 21

Other shapes, such as curves, can be difficult and may require marking out first. A white chinagraph pencil is ideal for this. Any uncut lines can be wiped off with a damp cloth later

STEP 22

I like to include text in this type of work, and there are a number of ways to achieve this. ‘Blocking’ is one; you will no doubt find others. You could use text to personalise the item if giving it as a gift. Otherwise just have fun with it. There are no rights and wrongs, and what you decide you want is fine. Don’t get too hung up on accuracy or neatness. Look at examples from other craft/art forms and you’ll note the ‘hand-drawn’ look is acceptable

STEP 23

Once finished I treat the surface with a UV protecting matte lacquer to ensure the colours last as long as possible. Make sure any lacquer is compatible with acrylic paint. Your art supplies shop should be able to advise you on the best type


Briony Darnley

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Weekend Projects , Andy Coates