Looking for some old slag – at the Fernhurst Furnace

If you like some old slag then last weekend was your thing, at the annual Fernhurst Furnace Open Weekend. With a forecast for bad weather as the remnants of hurricane Katia lashed the country I wasn’t expecting much, but in the event, apart from the odd shower, we escaped the worst of it and the show went on. Sheltered in the woods on the track down to the site of the old Wealden Furnace I hardly noticed the wind.

Unlike many of the shows and events that I do, this one is not commercial, being primarily a small community based event and has another purpose, to raise awareness of the remains of the North Park Iron Works which operated  on the site for over 200 years.  One of dozens of Iron Furnaces in the Wealds of Sussex, they were eventually put out of business by the successful use of coke for smelting in the Ironbridge gorge, releasing the ironmasters from their dependance upon charcoal as a fuel source and allowing iron working to be concentrated on massive sites.

It’s hard to get a sense of the size, noise and activities of the iron workings from the remains on the site you can see today. Almost all of the Wealden Furnaces have disappeared leaving little trace which makes this site something special. The most obvious feature is the size of the furnace pond and it’s retaining bank, availability of water being one of the biggest restrictions on the Wealden sites. Below the sluice it is possible to make out the remains of the wheel pits, the casting floor, furnace base and the charging ramp. You can even just make out the remains of the casting pit for the naval cannon that were made on the site.

This model gives a better feel for the scale of the buildings in the photo you can see the actual wheel pits and stream just to the right of the one in the model. You can learn more of the history of the site at the furnace website.

The iron industry in the Weald existed from Roman times (and probably well before that) but as the industry in the north of England scaled up in the 18th Century the Wealden Ironmasters were forced to rely upon their iron making and casting skills to compete. As well as making ‘pig’ or lump iron for the hammer forge at Pophole on the nearby Wey the furnace cast cannon for the Navy.  This cannon is a good example of the type that would have produced by the Wealden furnaces (though this one is not from this furnace).

The two sites, furnace and forge needed to be separate because of the restricted supply of water (power) and charcoal (fuel). This cannon ball was found in the grounds of a cottage close to the hammer forge at Pophole on the Wey and was most likely cast from pig iron smelted at the furnace 2 miles away.

Making iron from the ore requires a lot of heat, fuel and plenty of power on hand so we weren’t able to demonstrate it over the Weekend. But Fergus and Penny from nearby Butser Ancient Farm did take us right back to the start of the technology by demonstrating how to smelt copper from ore, very much the same principles which were refined (pun entirely intended) to smelt iron.

Fergus used Malachite which is a very rich copper ore, copper carbonate, the oxide of copper giving the mineral it’s characteristic green colour.

To turn the green malachite into copper the temperature in the clay furnace needs to reach almost 1400 degrees centigrade which is achieved using good quality lumpwood charcoal and plenty of air blown through the fire from the hand powered leather bellows.

The green tinge of the flame indicates that the furnace is reaching the right temperature and the copper in the malachite is being released. This happens as the charcoal creates a reducing action by burning and producing carbon monoxide that then steals oxygen from the copper oxide to make copper.

At the end of the process the crucible containing the molten copper and remains of the malachite mixed with some charcoal is removed from the furnace to pour into moulds.

Though in this case the copper pulled a disappearing stunt and flowed to the base of the crucible where it stuck fast until cooled and released by Fergus – though it does look more spectacular in this shape and contrasts with the original green of the malachite.

I was impressed that you can produce your own metal with some clay, charcoal, a pair of bellows and some ore. You really could try this at home. Though it might be better to try it with Butser ancient farm first and you can find out more about their courses including Fergus’ metal making on their Butser Ancient Farm website .

The title of this post is a shameful attempt to attract hits and maybe even readers via the search engines, though whether they will be impressed with my old slag is doubtful. Given the centuries of iron working at the site, and at nearby Pophole hammer forge, slag tends to turn up all over the place and would have been used to fill in the notoriously poor Sussex roads, but I found my old slag in the end and a fine example it is too. I shall have to leave the rest of the weekend to another post.

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Bluebells and Charcoal Burn – the ring of fire

The bluebells are coming on strongly in our restored Hazel Coppice (better than the Hazel unfortunately) and I stopped to take some photos on my way to make charcoal yesterday. It’s hard to capture the delicate colours and the sun was a little too weak to do justice but you get the idea, I hope.

The burn in my oil drums went well, no great surprise as the weather is perfect for it. With the long dry and warm spell having reduced the moisture in the wood significantly the burn is shorter and the yield is higher.

One drum burnt a lot slower than the others and getting bored with waiting I turned the heat up (opened up the vents around the bottom) and with the top shut down it produced an almost perfect ring of fire as the volatile woodgases were burnt off.

Very pretty to see – don’t try this at home. No really – to get the ring effect I shut the top of the drum down for a short time which suppresses the fire and the gases are collecting unburnt. Then on opening the top the gases mix with more oxygen and leap from the drum. Worthwhile wearing a helmet and gloves unless you like the singed eyebrow effect.  But it’s all wasted heat which would be better used in the burn – I need to move to a simple retort system in which the wood is baked in an oven and the gases are used to help improve the burn. But that’s another project!

Alright I admit it. This post is just an excuse to mix the photos of the bluebells with the flames – and I like the effect of the two very different textures and colours.

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Making Charcoal – First burn of the year with Birch, Sweet Chestnut and Oak

 

The first charcoal burn of the year is always a bit of a struggle and somehow I manage to forget just how damp everything will be. One day of relative warmth is not enough to shake of the winter yet.

 

For this burn I had help from Fergus (from Butser Ancient Farm). Fergus is using charcoal to smelt and forge and contacted me to discuss some comparative smelting tests using charcoal from different wood species. I couldn’t help being interested and one advantage of using old oil drums as kilns is that I can burn different woods in each drum so we decided upon Birch, Sweet Chestnut and Oak.

 

Unfortunately the first burn of the year is never too highly organised ( must make a note not to make the first burn a demonstration in future!) and it took a while to fetch the timber and then cut and split it.

 

and I hadn’t counted on the bins being quite so hard to get lit but after quite a struggle we got three bins going.

 

It’s the first time I’ve compared different woods burning side by side. Once the Sweet Chestnut got going it burnt very hot and fast with a lot of gas coming off – at one stage the top of the bin looked more like a gigantic gas ring than a kiln – really don’t try this at home, it is very easy to lose your eyebrows!

 

The Birch was a little slower to get going and produced a lot more white smoke – probably reflecting the difference in relative moisture content between the woods. As expected the oak drum was the slowest to burn – oak being a very dense wood it typically burns more slowly than the lighter woods.

 

Having left the bins sealed to cool overnight I unloaded them the next morning.

 

As I’d expected from the way the burns went the Sweet Chestnut bin was the best, producing large lumps of charcoal and very few brown ends (the logs which are not completely converted to charcoal). But the birch bin was also very good with a similar amount of charcoal, albeit in smaller pieces, and as expected the oak bin produced the least in volume.

But once I got the sacks of charcoal back to the workshop and weighed them I was surprised to discover that though the volumes clearly differed the weights of charcoal from each bin were very close. Chestnut – 11.5 lbs, Birch – 11 lbs and Oak -10.5 lbs.  The oak being significantly denser charcoal than either the birch or the chestnut.

Fergus – if you are reading this – the charcoal is ready to be collected and I’m looking forward to finding out how it does ! Hope you’ve recovered from the smoke inhalation!

 

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Where does your wood-ash go?

It’s around about this time of year that I reach peak production of ash from our two fireplaces. About 1 to 2 percent of the firewood remains as ash and this is generally thought of as a waste product. But not for much longer!

The main constituent of the ash is calcium carbonate (between 25- 45%) with potash (potassium) less than 10% and phosphates between 1 and 2 % and trace elements of magnesium, iron etc. Woodash can be used effectively as a fertiliser on your garden. The alkaline nature is a liming agent raising the soil pH and allowing the plants to improve their uptake of available nutrients (though you wouldn’t want the soil to become too alkaline, not so useful if your garden is on chalk, but great if you are on sandy peaty soilds). The woodash also provides nutrients through the  potassium, phosphates and the other trace elements.

 

But as well as these chemicals the ash often contains small pieces of charcoal, the chared remnants of the wood not completely combusted. This is pure carbon which will last in the soil without decaying and helps to provide structure to the soil as well as aiding in moisture retention. Recent studies indicate that the charcoal also plays an active part in fertilising the soil by acting as host for microbial action once it is activated.

 

As the woodash is alkaline in nature it’s best not to apply it directly to plants, though I’ve developed a habit of spreading it on the weeds in the winter in the hope of discouraging them. Keep it dry until you use it as the nutrients can easily be leached out by the water. I’ve heard it’s also quite effective as a mulch and a slug/snail deterrent.

So thats potash, phosphates, trace elements, carbon capture, water retention and management and slug deterrent – this is good.  But of course the major element that its missing is Nitrogen. Now where could you find a concentrated source of nitrogen that would be better off on your vegetable patch than being fed back into our rivers and streams?

No I’m not taking the p**s! Its serious, a recent study in Finland has found that the combination of woodash and urine acts as an excellent fertiliser delivering 4 times the yield of tomatoes compared with unfertilised plants. And thats without considering the longer term benefits to the soil structure and fertility. I can see our greenhouse will be fitted with appropriate blinds this summer!

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Earthburn 2010 – photos on gallery page

If you haven’t had enough yet I’ve uploaded more of the photos from the Earthburn to a gallery page. Either select the Gallery tab above the blog title banner or follow the link here.

Earthburn Gallery

These only cover the building and burning of the charcoal kiln, the photos from the coppice courses will follow soon.

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Earthburn 2010 – Day 2 onwards

As you will have realised, I didn’t get the chance to post any further updates during the Earthburn last week. Now finally back home after leaving the Earthburn on Friday and going down to the Weald & Downland Museum for the Steam Festival (where the smoke smelt entirely different but I probably fitted in quite well) I can catch up with the story.

The burn started slowly and deceptively gently. Here Mr Jameson tends to the hay and soil covering as the burn creeps down the stack. By late on the first evening all was going well and in the ‘hurry up and wait’ nature of things it looked as if the hard work was over for a while. By just after midnight the top of the kiln was starting to collapse noticeably as the top tier of wood burned. But  I decided to get some sleep and missed all the excitement in the next few hours.

Under the gently exterior the burn was gathering pace and beginning to build up heat. Around about 3am the burn broke through the top of the kiln as woodgas was released and ignited. For the next hours the team fought bravely (or so they told me over breakfast) to contain the burn using water, soil and a few bits of tin lying around the site whilst the heat was gradually reduced and the last of the woodgas burnt off. In my opinion birch has something of a habit of doing this, especially when it’s still slightly green – quite easy to lose your eyebrows and even with my small oildrum kilns it can just about blow the lid off when the gas mixes with oxygen. So I can imagine that controlling a stack of several tons of birch 8 feet tall and 20feet across is quite a dangerous occupation. No wonder a few charcoal burners used to go missing from time to time.

So I missed all of the dramatic photos in the early hours of the morning and by breakfast time it looked as if everything was under control – except that the kiln had reduced in size dramatically overnight.  Alan Waters and Mark Cox debate the next course of action.

Peter Jameson demonstrates just how comfortable the one legged charcoal burners stool can be when you’ve been up since 3am.

One of the team drew this very authentic sketch of the scene using willow (artists) charcoal to hand.

As Thursday (day 2) drew onwards the kiln became progressively more peacefull with the last of the moisture and volatiles driven off the fire is burning right down to the level of the hearth and the smoke is starting to turn bluish. It prooved to be a quieter night though still busy as the hay and earth covering is constantly being tended to whilst the wood contracts under it to prevent the fire breaking through again.

The winds were light throughout the burn which was helpful, but it doesn’t need much movement to fan the flames and make it hard to control the burn evenly around the kiln so these screens were erected, gate hurdles covered in hessian, to reduce the air flow over the kiln.

Jimmy on watch over the kiln inspects the drawing his son Jacob has made of the scene, complete with his dad’s coffee mug.

Unfortunately I didn’t get to see the kiln opened as I had to leave for the next show on Friday. It’s not as simple as leaving it to cool, as you do with metal kilns and oil drums as it’s not possible to completely seal the covering. So the fire has to be put out by using water – though its the boiling of the water into steam which actually stops the fire by reducing the heat and excluding the oxygen, rather than by dowsing or drowning the fire. Once it’s been ‘steamed’ the coals can then be collected, sieved and bagged.

Alongside the charcoal burn were a number of greenwood courses taking place and some demonstrations – including the polelathe so I’ll post on these next.

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Good weather for making charcoal….

…and good weather for selling it as well it seems. During the summer months my sales are limited by the low prices offered in the local supermarket. I notice there is a lot of cheap lumpwood charcoal from Namibia at the moment which is labled as FSC. I can imagine that Namibia is great for making charcoal being hot and dry, but overloaded with sustainable forestry is not how I think of it, let alone the journey halfway round  the world to get it here and then sell is at half the price of local products. But I won’t get started on that hobbyhorse – its alright for me as I am only doing it to process unwanted branchwood from the management work on the Lynchmere commons and I only supply one local hardware shop in nearby Liphook or sell it direct from home. I wouldn’t want it to become to much of a job as even now it can be quite demanding – my sales are mainly to recurrent customers and in weather like this they are planning BBQ’s . Having failed to get ahead in the spring I am now struggling to keep up.

But at least the wood has dried well and with less moisture to drive off the yield is higher than I normally manage from my small oil drums.

I am normally making charcoal from the birch trees on the commons, but this winter we didn’t have much birch left over so I’m using different woods whilst the fresh birch dries a little. It’s always interesting to see how different woods turn to charcoal as they have remarkably different densities and the original structure of the wood is preserved when the wood is converted well.

This is well seasoned sweet chestnut which makes excellent charcoal – but it does need to be seasoned for a couple of years first. The chestnut charcoal seems to be particularly light, needing a higher volume to reach the same weight, though charcoal is normally packed by volume and not weight (by local producers) as it will change weight as it dries or absorbs water from the environment around it.

…..and here is a piece of simimarly well seasoned oak…..

while this is relatively freshly felled (6month) hazel. I know of some charcoal burners who can pick out the coals from a bag and identify each wood.

While I was bagging the charcoal I noticed that most of the birch trees are recovering from having their leaves stripped off by the caterpillars, though it looks as through about 10-20 of the smaller and weaker trees may have succumbed to the attack.

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