News: How to cast a Tree

17 July 2014

This has to have been one of our more unusual and challenging projects in recent years. Casting 'Still Leaping' for Antony Gormley in 1993 was something of a departure for us at the time and tested our mettle to the limit (pun intended). Since then we have cast objects as diverse as scaled down models of the Angel of the North, huge patterned columns, delicate balusters, carved cherubs and of course 12 tonne machine beds. So what is involved in casting a whole tree trunk and lower branches in one piece - read on and find out.

The project was brought to us by artist Geoff Wood. Essentially he delivered us a whole tree about 6 metres long with a diameter of about 1.8 metres. The trunk had been cut into two halves and the tops of the branches removed. The first thing to do was, working closely with Geoff, agree which sections of the tree we could include in the casting process and how we could fix them together ready for casting.

Geoff working on top and bottom halves of the Tree Geoff working on top and bottom halves of the Tree height=

Manufacturing a casting this size needed to be done in the traditional way in a pit in the foundry floor. The process would follow several stages; Getting the tree on to a bed of sand in the foundry and reassembling it Creating what would become the bottom part of the mould in a moulding box, turning it over and placing it at the bottom of the pit Carefully placing the tree back into the bottom part of the mould in the pit Building up the top of the mould in sections over the areas of tree still exposed Removing the mould sections so that the tree could be lifted out Lining the inside of the mould with one inch thick polystyrene strips to create some metal thickness Making sand cores on the inside of the moulds lined with polystyrene Putting all the sections of the mould back into place over the sand cores Covering the mould, clamping it in place and putting weights on top to help hold it in place during the casting process. Melting 12 tonnes of iron in two ladles and pouring it into the mould. (The previous stages took five weeks - melting the iron took three hours and pouring it took 90 seconds.) Allowing the iron to cool, digging the casting out of the sand and fettling it. The finishing work was again done in close collaboration with Geoff to ensure the final result was to his satisfaction

Tree in the sand at the start of the mould making process Geoff working on top and bottom halves of the Tree height=

The mould in progress

Geoff working on top and bottom halves of the Tree height=

Pouring the iron into the mould

Geoff working on top and bottom halves of the Tree height=

Having reduced the process to 11 bullet points, I should just stress the level of skill, knowledge, hard work and sheer enterprise in tackling and successfully completing such a challenging project. And not just on our part, but also on the part of Geoff, his associates and his clients. This project was never a given! The tree is due to be unveiled at its permanent location early next year, so it would be inappropriate on our part to show photographs of the finished product until after that. We will at that time post a more detailed account of how it was all achieved with photos and video. In the meantime you may be interested in some stats about the project.

As mentioned the overall length of the tree was 6 metres and the trunk diameter 1.8 metres. The spread of the branches at the widest point was just over 3 metres. Before the sand cores were removed the casting weighed 18 tonnes and the finished casting without the sand cores weighed 9 tonnes. We used 12 tonnes of iron, which took 3 hours to melt at 1,500 degrees centigrade and 12 taps into two separate ladles. The mould used 80 tonnes of sand in total and was clamped into place before 50 tonnes of weights were placed on top. The iron was poured at 1,360 degrees centigrade and took 90 seconds to fill the mould.