Monday 9 July 2018
When designing a decoratively shaped bowl, such as the one shown in this project, it helps to draw outline shapes and patterns in a sketch pad. These shapes give you a visual aid for how your finished item will look. Once the desired shape has been selected, the profile can then be copied onto a length of timber the correct size. To do this, select a piece of paper the same size as the timber, fold the paper in half and then in half again. Draw a quarter of the profile on one side and cut out. When the paper is opened out, an equal pattern will emerge. The shape is then cut into the blank, before any turning is done. The size of the internal bowl will be dependent on the width of timber being used: I chose a piece of sycamore (Acer pseudoplatanus) measuring 165 x 296 x 50mm, which allows for a reasonable size bowl. Rather than using a square piece of timber, I have used a rectangular piece, which creates two long 'wings'. This makes the turning slightly more difficult, but produces a very pleasing shape. Should you wish to avoid turning uneven shaped timber, this bowl could be turned from a round bowl blank measuring 295mm in diameter and cut to shape once turned.
The decoration I have applied is called 'sgraffito', which is a decorative technique used in pottery, glass and painting. It is where two layers of different colours are used: the top layer is then scratched in to reveal the underneath colour. For this project I have used a black base colour and gold iridescent paint for the top coat. I have used a rubber 'sgraffito' comb, designed for this technique, to scratch a small straight-lined pattern through to the base coat.
To give the decoration an Art Deco feel, I applied some low tac tape in straight lines leading from the edges of the wings to the start of the rim of the bowl, before applying the top coat of paint and creating the pattern. When the tape is removed, solid black lines emerge, which adds to the overall design.
Place your bowl template on a piece of sycamore measuring 165 x 295 x 50mm. Secure in place using pieces of masking tape. You can then draw around the template using a permanent marker pen
The next step, using a bandsaw, with a thin blade fitted, is to cut along the black lines to create the finished shape
You can then drill a hole, the correct size for your jaws into the top face of the bowl blank. Clamp the timber to the pillar drill to hold securely in place while drilling
Mount the timber on the lathe, position the toolrest and secure tightly in place. Stick a piece of masking tape over the toolrest and mark where the edges of the rotating wood start. This will help for positioning your tools for beginning each cut
Cut a spigot the correct size for your jaws. Here I am using a skew chisel laid on its side to create a dovetail
Mark where the underneath of the bowl will be and, working from the outer edge, reduce the thickness of the wings leaving step cuts for the bowl to be shaped – see drawing
When the desired wall thickness has been achieved along the wings, shape the base of the bowl. Cutting from the spigot, with the grain and towards the wings, remove the step cuts produced earlier. Blend the bowl shape into the wings to form a crisp transition. A long-grind 10mm bowl gouge can be used for this
When the shape of the bowl is satisfactory cut a 'V' groove to define the foot. A fingernail-profile spindle gouge is suitable for this and will create a crisply cut groove without torn grain. Sand the bowl section and the solid part of the wings on the lathe working through 120-400 grit abrasives
Sanding the underneath
For the underneath of the bowl start cutting from the outer edge and work towards the centre, leaving step cuts where the bowl shape is to be turned. This will allow the wings to be shaped and cut to the required thickness, while still having the bulk of material left for support. When the wings are the required thickness you can start to shape the bowl – a rough profile of the bowl shape should be evident from the step cuts being left, while cutting the wings. To refine the shape of the bowl, start cutting from the centre, removing the step cuts as you go. Blend the transition between the bowl and wings.
A long-grind bowl gouge is used for this. Start at the foot and using a bevel supported cut, work towards the wings. The tool is then rotated to shear scrape the solid section of the wings. This is done by rotating the flute of the tool towards the wing, lowering the handle to bring the swept-back grind of the tool into contact with the solid section of the wings. The transition from bevel supported cut to shear scraping is done in one fluid movement to create a clean cut. Do not shear scrape beyond the solid section of timber; this section will be hand sanded off the lathe using a sanding block.
Remove the bowl from the lathe and apply masking tape to the sanded bowl section, this will protect it from being scratched when sanding the wings. Using a large sanding arbor or similar, hand sand the wings. This is easier when sat on a flat surface covered with non-slip matting. Sand in the direction of the grain and work through your usual grits ensuring all marks are removed before progressing to the next grit
Mount the bowl on the lathe, using the chucking spigot cut earlier and true up the front face
Remove from the lathe and hand sand the surface, using the same grits and process as for the underside. Paint with acrylic black paint mixed with flow medium. This will produce a smooth coat, which will only need a gentle rub with 1,000 grit abrasive when dry, to remove any imperfections
Mount the bowl on the lathe and cut a 'V' groove, through to clean timber, at a diameter of 135mm. A three-point tool is used for this
Apply strips of 3mm-wide low tac tape running from the outer edges of the wings to the 'V' groove. Stick some masking tape around the 'V' groove to avoid contaminating with paint
Apply a thick coat of gold iridescent paint mixed with flow medium to the surface and using a sgraffito comb, scribe a crisscross pattern into the paint. This removes the gold paint revealing the black base coat and creates a pleasing pattern
For this paint effect I have used Jo Sonja acrylic paints. I used black for the base coat and iridescent gold for the top coat. Both have been mixed with flow medium, which 'waters down' the paint without it losing its viscosity. The thinner paint allows you to achieve a smooth, flat finish. Once the base coat is dry, sand gently with 1,000 grit abrasive, this will remove any blemishes. Clean the surface with tac cloth and apply some 3mm-wide low tac tape in straight lines from the outer edges to the cut groove. The tape needs to be securely adhered to the surface to prevent seepage; however, should seepage occur, this can be easily touched up with black paint once the finished pattern is fully dry. Apply some masking tape around the 'V' groove, pushing the edges into the groove; this will stop the gold paint from soiling the groove.
Iridescent paint is milky in appearance, only showing its colour when applied to a dark surface. If applied thickly this milky appearance remains. For the sgraffito technique a thick coat of paint is required and to prolong the working time requires mixing with flow medium. Apply to one wing at a time and create the crisscross pattern with a rubber sgraffito comb. The comb removes the wet paint, leaving the base coat showing through. Allow the paint to dry thoroughly before removing the masking tape to reveal crisp black lines.
When trying a new painting technique it helps to practice on a scrap piece of wood to help you perfect the technique before applying it to your turning. If you don't like the pattern or choice of colours you can black out and try another combination.
When the paint is dry, remove the masking tape to reveal the black lines. If any gold paint has seeped under the tape, this can be touched up
Next, remove the centre of the bowl leaving a 2mm wide ring of black paint at the rim. A 10mm standard-grind bowl gouge is used for this. Create a small cove leading from the ring of black to the start of the bowl. Sand the bowl centre using the same grits as before
With the bowl still on the lathe and with the spindle locked in position, hand sand the edges of the bowl. This will remove excess paint and also smooth any bandsaw blade marks. Work through all the grits using a sanding arbor for support. Try to avoid rounding over the edges at this stage
Remount the bowl using your preferred method and remove the chucking point: Here I am using a vacuum chuck, which allows the taildrive to be removed giving better access to the foot
To finish the bowl, apply several coats of finishing oil. The finished project should look something like this