We took a family day out to York at the weekend and took a walk along the walls. Here’s a beautiful example of an unplanned biocidal effect. The copper in the plaque has been slowly dissolving in the rain and washing down the wall keeping this section completely clear of biological growth. Unfortunately the strong green colour just below the plaque wouldn’t really be considered acceptable!
Lynda and Philip Skipper were at the Natural Stone Show in London last week, presenting results of the first stage of their stone bioreceptivity project (in other words, measuring how quickly stones go green), funded by Historic England.
Edit: If you would like to see our presentation it is now available at https://www.stoneshow.co.uk/conservation-day in session 2.
We’ve completed the pilot phase for our study! In this phase we looked at all the different methods of testing stone bioreceptivity in the literature.
We then selected one to take forwards for looking at different stone types and with a few tweaks to the methodology we have a protocol which will work for most types of stone used in the heritage field. Next step is to start looking at adapting this methodology to give us a lab based test for biocides which will show whether they change the bioreceptivity of the surfaces, oh and get the pilot phase written up and published!
As we mentioned in our launch post for the Historic England project we are looking at three heritage stones, here’s a little background on them…
Foggintor Granite
Foggintor quarry, originally known as Royal Oak quarry, is located near Princetown on Dartmoor (UK), the quarry is now closed but the stone is still available from stock. The granite is a biotite-bearing syeno-granite pegmatite with crystal colours primarily ranging from medium light grey to greyish black . Stone from this quarry was used in the main column of Nelson’s column as well as many other notable London buildings.
Howley Park Sandstone
Howley Park sandstone is still quarried near Leeds (UK), it’s a brownish coloured dolomitic sublithic wacke-stone. This stone has been used in heritage sites such as the Coliseum Theatre in Leeds and Wentworth House in South Yorkshire.
Jordans Basebed Portland Limestone
Jordans Basebed limestone originates from the Isle of Portland (UK). It’s an oolitic limestone containing small fossil shell fragments with a creamy white colour which is typical of Portland limestones. Portland limestones were widely used by Christopher Wren in the rebuilding of London following the Great Fire in 1666, it is also the stone of choice for the Commonwealth War Graves Commission for headstones and so can be found globally.
Exciting news! Historic England Commissions have agreed to fund a 3 year project looking at ways of standardising testing for bioreceptivity of stone and also looking into sustainable alternatives to current biocides. We will be looking at a limestone, a sandstone and a granite as part of our studies and will post updates as regularly as we can!