Carve and Fume a Celtic Cross archive

Friday 15 January 2010

Steve Bisco borrows from British heritage to produce this stylish Celtic cross, perfect for a weekend project


The Celtic cross is an evocative symbol of British past, conjuring up images of mist-shrouded churchyards sitting on rocky headlands where saintly missionaries from Rome converted the ancient Celts and Saxons from their pagan ways.

The conversions were not completely successful because Celtic crosses were richly decorated with spiritual symbols from the old Celtic religion, which they simply recycled into their new one. The missionary bishops of the Dark Ages were fairly pragmatic about these things, so I have allowed more than a touch of sorcery to creep into this design.

You can carve this cross in a weekend from a piece of green oak (Quercus robur). However, it comes with an optional extra. If you want to give it a real feel of the Dark Ages you can blacken the oak by the process of fuming, which will give the effect of aging it by many centuries overnight. The choice is yours: light oak or dark. Carve it first, and then decide. Perhaps the Celtic spirits will guide you!

Shaping the cross

1. Make a full-size copy of the drawing and trace it onto a piece of green oak 330 x 178 x 18mm (using carbon paper. If you intend to fume it later, make sure your oak is all heartwood and does not have any sapwood in it as it will not darken when fumed.

2. Cut round the outside of the pattern with a bandsaw or jigsaw, and trim up the edges to a smooth finish with a spokeshave and a flat chisel.

3. Use a jigsaw, coping saw, scrollsaw or fretsaw to cut out the sections inside the ring. Keep the work moving along as the heat will scorch the sides of the cut. Use a half-round file or abrasives to remove any scorch marks.

4. Fix the cross to a backing board by screwing from the back with two short screws, and clamp the board to the bench. Cut the surface of the ring of eternity down to 6mm below the surface of the cross with a flat chisel.

5. Draw two lines 5mm in from the inner and outer edges of the ring, leaving a 5mm strip in the middle. Cut a U-shaped cove along this strip with a 4mm No.9 gouge, taking care to keep the cutting edge on the downstream side of the grain in each direction. Care must be taken to be as neat as you can as the ring is a prominent feature of this cross.

Grounding out the pattern

6. Grounding out (cutting away the background to leave the pattern standing out) is the most time-consuming and least exciting part of a bas-relief carving, but it needs to be done carefully to get a good result. Start by using a V-tool to cut around the pattern lines to define the edges. Do not be tempted to bost down vertically just yet as the pressure may break out parts of the pattern. Be aware that the thin cross-grain sections of the pattern are particularly vulnerable to breakout.

7.With the V-cuts relieving the pressure, you can now make the edges vertical with paring and bosting cuts using fine chisels. Take particular care with the outer border. You can clamp a steel rule along the straight edges to give you a clean straight cut. Cut away the background areas to about 5mm below the top surface, taking care not to lever up parts of the pattern in the smaller gaps. There are some very narrow gaps between the knotwork and the sides, so you will need chisels as small as 2mm in width.

Carving knotwork and symbols

8. Mark the overlaps on the knotwork, then work them down so the ribbons appear to flow smoothly over and under one another without disappearing into the background.

9. Use a No.5 gouge to carve the central trinity knot so the three rounded strands seem to wrap into one-another like an endless cord. The star is carved by creating angular faces with a flat chisel. Try to get good sharp edges as the shadows will define the shape.

10. To carve the crescent moon, scoop out a hollow on the right-hand side with a No. 5 gouge to leave a crescent on the left side. Give the inside of the crescent a sharp edge to create a strong shadow, and round over the outward side. The four-sided symbol representing earth, air, fire and water, is carved using a flat chisel, cutting from the centre down towards each of the four edges.

Finishing the carving

11. You can finish the cross in its natural light oak colour by rubbing it hard and vigorously with a dry cloth to bring up a natural sheen. This is better than using abrasives, which tend to leave a dull finish and soft edges. If you do not intend to fume it, you can give it a coat of wax polish to bring up the colour. However, if you have decided to go the full Celtic, do not put anything on the surface just yet.

Back to the Dark Ages

Fuming with ammonia is the traditional way of darkening oak. It looks more natural than stains because it causes the same chemical changes in the natural tannins of the wood as ageing does.

Fuming effectively copresses the chemical changes of centuries into a just a few hours, so if you want to go for that real Dark Ages look without waiting a thousand years, get out the ammonia…

12. Fuming is easy, you just need some sort of container that you can make airtight with the wood inside it, such as this plastic tub. I am using polythene sheet to cover the top, sealed round the edges with double-sided tape. Pour four or five tablespoons of household ammonia into the bottom of the container. Place the cross clear of the bottom on a couple of wooden supports, allowing the fumes to flow freely around the wood. Cover and seal the tub.

13. The time taken for fuming depends on a number of variables: strength and volume of ammonia, temperature, and the darkness you want to achieve. So it is more of an art than a science. With household ammonia it should take 12 to 24 hours to go from pale and interesting to dark and mysterious.

If it is too slow to darken, add more ammonia and leave it a few hours more. As we are going back to the Dark Ages, there is no danger of leaving it in too long.

When the cross is fumed, it will have aged centuries in a day and will look like a relic from the ancient past. This process is such a simple yet effective one

14. Give the raised pattern a rub over with a good wax furniture polish like Antiquax, leaving the background unpolished for contrast. Now hang it on the wall, and admire your handiwork.

Woodworkers Institute

Tagged In:

Stev Bisco , Celtic cross , weekend project , fuming

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Helpful Hint

1. When you are carving a pattern with dead straight edges, like the border on this cross, clamp a steel rule along the line of the cut. This will help you keep the edge straight.
2. If you accidentally break out part of the pattern while grounding out, try to retrieve the fragment and glue it back in place, or graft in a new piece to match it. Once the glue has set, you can usually carve the pattern without the repair showing.

Carving With Green Oak

Green oak is much easier to carve than fully dried oak. Its only drawback is its tendency to warp as it continues to dry out, so avoid pieces with knots or a contorted grain pattern.
You may not find green oak on sale at a timber merchant, so look at the Classified section at the back of this issue, in the Yellow Pages, or on the internet for your nearest sawmill.
Just one word of warning. Sapwood (the softer new growth on the outer edge of the tree) does not respond to fuming and will stay pale, so only use the heartwood if you choose to fume your cross.

A Word On Ammonia

The easiest way to buy liquid ammonia is as the household ammonia sold by ironmongers and hardware stores. If used undiluted, this is strong enough for fuming oak, even though you may have to leave it in the fumes a bit longer depending on the strength. It is rather pungent, but safe enough to use if you follow the safety instructions of the manufacturer. Wear eye protection and gloves when handling, and use it in a well-ventilated place.

Diagrams Click an image to enlarge