Category: Techniques

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Paying the tanning mixture into Jantje’s sail; the sail before tanning; heating the tanning mixture. Click on the images for a larger photo

In weblogging, one good thing often leads to another. Earlier posts about the restoration of a steilsteven tjalk named Jantje explained that she still had an old sail in good condition when she was acquired and that expert Hermann Osterman had tanned the sail using the old methods – and naturally a number of readers asked for more information.

I’m delighted that Hermann has kindly sent us the photos above, and the description that follows. In fact, I’m pretty sure various tanning methods have been used over the centuries and these days I gather the favoured product is standard wood preserving stains such as Cuprinol – but Hermann used the traditional cutch – in this case tannin-laden extracts from the South American quebracho tree (see definition 1, definition 2).

Here’s what Hermann has to say:

‘The tanning of a traditional sail cannot be performed in a boatshed: you need a flat, clean cement floor, or better, short-cut grass, and also a copper of about 80 litres capacity with a fire chest. In the days of fishing under sail nearly every fishing community had a tan house or a such like arrangement.

‘I have written a detailed account on the common methods, recipes and materials used for preserving nets and sails that appeared in  the journal Maritime South West, which is published by the South West Maritime History Society. The journal for 2009 is available at a cost of £12, plus postage from society member David Clement, who can be emailed at dclement1@toucansurf.com.

‘Jantje’s sail had been stored with other equipment in her hold for many years, and I must say it represented a rare opportunity to tan the sail, which was an example of the old craftsmanship. Indeed, one should seriously consider whether it is right to tan an old sail, for it should only be done if it is in such good condition that it will be possible bend it on for sailing once again, and if you have reason to expect it will benefit from the treatment as well as taking on the traditional colour of a tanned sail.

‘In fact, Jantje’s sail had been made from linen cloth in the 1920s or ’30s had been left untreated and had become greyish colour, in overall it was good enough for further use as a sail.

Based on my own experience of sail tanning, I chose a solution consisting of about 1.5kg of quebracho powder to 10 litres of water, which was simmered for a little over two hours to extract the tannins (that’s the minimum; longer is even better). The temperature should be maintained at just up over 70degC; it is important not to overheat the liquor. Some 10g of soda is added after two hours.

Before treating the sail, I wetted it with water. This has to be rainwater, or water from a well, river or sea-water. The whole procedure, with wetting and dressing the other side of the sail took at last about 8 hours.

Usually one cannot expect to achieve a good deep colour from a first tanning treatment – the colour seen in old sails is the result of repeated dressings, but Jantje’s sail took on a particularly good rich shade.

‘Before tanning a sail it’s important to test the process on small patches of canvas, and to record the steps, quantities and timings of the procedure, and to choose the tanning mixture and treatment in line with local traditions.

‘Nowadays cutch is supplied in square, round, and irregular pieces, which may be pale red, pale brown, or nearly black, and often having a sweetish after-taste, and is also available as a highly soluble dyeing powder. The quebracho powder (trade mark Unitan) I used for Jantje’s sail, is extracted from the hardwood of the South American trees of the same name and is available in a range of different readily mixed colours.

‘Some alternatives for making cutch include oak and birchbark extracts, natural ochre powder and certain fatty liquors used in the leather industry.

‘Hermann Ostermann’

Thanks very much Hermann – that’s tremendous!

Tanhouse at the Fisheriesmuseum of Oostduinkerke