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.
