Monthly Archives: February 2012

‘RH 101…’

'Just before the penny dropped..'


‘A lesson in Humidity…’

The concept of ‘Condensation’ is a perfect example of humidity. The temperature at which this occurs depends on the level of moisture in the air. Inside this can be seen on window panes as the temperature of the glass falls, and outside, when the temperature drops, condensation can form on blades of grass, and given rise to the term ‘dew point’. Localised RH fluctuations can also affect objects and these can be simple things like sunlight or a radiator. Ever been in a stuffy attic in the summer? That’ll be the low RH then… Dramatic fluctuations can have dramatic results and cause canvas and wood to expand and contract at different rates to the paint layer, so cracks will appear and in worse cases flake and fall off. Among the many gadgets that are available to the humble conservator are those produced by the good people of Hanwell. A system of wireless units placed throughout the house sends info to our main computer to be displayed in a graph format. This is, once decoded; a quick reference for maintaining a happy house as you can monitor the temperature and RH from the comfort of an office chair before any decision about adjustments needs to be made. It did take a little while for my tiny brain to re-organise what I was looking at, hoping I didn’t try Katy’s ‘saint-like’ patience with me in the process! It’s a great tool to use, to gage results from days to weeks to months and even look at results from one year to the next. A handy warning light on the system tells you instantly when areas are in the danger zone and a relentless ‘bleep’ doesn’t let you forget!

‘An education in fluctuation…’

‘It’s all Relative…’

One of the most important aspects of conservation in an historic property is the concept of ‘Relative Humidity’ or RH for short. This was and still is a slightly tricky concept for me to get my head round, as maths and physics were never my strong subjects, so I’ll try my best to explain. (Mentor Katy D took great delight in firing off pop-quiz style questions, and watching me squirm…) Humidity is a fairly destructive mistress and can have a myriad of effects on a collection. A simple way to dive in to the subject is with a definition: ‘‘Warm air, holds more moisture than cold air’’. We keep an eye on this with percentages, and the dictionary definition of Relative Humidity is the ‘moisture content of the air, divided by the maximum amount of moisture the air can hold at that temperature’. 0 = very dry, and 100 = very damp. The target range for historic properties is between 40-65%. This safe zone is to fend off mould and corrosion when the air is too damp, and if too dry, the air can draw moisture from organic objects, and cause cracking in wood. So the temperature alone is not an issue but its effect on RH is. During winter months, when heating gets switched on, the air get’s drier and stuffy and it tries to absorb moisture from objects. Then when the heating is off, the air gets damper and the materials try to absorb the extra moisture. But, the RH can also increase when the temperature remains the same, such as on a rainy day. Of which we have many to due to our ‘unique intermittent weather system’.

‘Where it all began…’

A visit to Heelis was on the schedule this week, and for those non-NT members of the audience, it’s the nerve centre HQ epicentre of the National Trust located in the heart of Swindon. ‘Twas a strange visit, so draw nearer to the fire and I will tell the tale… The last time I had paid a visit to Heelis was about 8 months ago, at the end of my second training day when I had only been working at Dyrham for about 7 days. It was a naturally reflective moment walking through the doors, swipe-card turnstile, fingerprint scanner, retinal scanner and x-ray machine. (I made up the last three) Strange feelings were abundant, to look back and see how much I have achieved, in a relatively short period of time. Feeling a more confident and knowledgeable member of the team, than when I first started. And that goes for personal skills as well as professional ones. If I could time travel and whisper in the ear of the ‘me that was then’, I’d probably say, ‘‘take it easy dude, it’s gonna be an awesome year.’’ Having said that if I were granted time travel, talking to myself wouldn’t be high on the list of ‘things to do’. (In X-factor terms, it would be at this point where a misty-montage of black & white footage, documenting my ‘journey’ would be shown, along with a power ballad soundtrack…)

My visit was at the request of Passport project manager Claire Poulton, whose next wave of trainee’s on the ‘Passport to Your Future’ course were being put through their paces. I had a 40 minute slot, and was advised not to prepare anything, so to ‘keep it casual’ (on reflection if I had been any more ‘casual’ I would have turned up in PJ’s and slippers.) Having a sudden mild attack of butterflies, it was time for my bit and I cursed my casual-ness as I had forgotten the dry-ice and walk-on-intro music. How time flies when you’re having fun, and also when you’re rambling on a bit. It was a good excuse to reflect on my experience so far, as it has, without shadow of a doubt been the best 8 months of my working life. I feel honoured to be part of the staff at Dyrham, and still find it difficult not to hug people when I see them! To my amazement my time was up before I knew it and there were even questions too! (Quick ‘hello!’ to newbie Alison who’s been following the blog.)

‘Reading between the lines..’

‘What, more books?’

Yes indeed, I had the privilege of cleaning some more of our Great Hall books and found some very interesting things therein. Being careful as much as naturally curious, I’ve been checking most of the books as I go, to keep an eye on the inventory numbers so they get returned to the shelves in the right order. This cuts down the possibility of getting muddled and is a good excuse to have a quick scan of the content. Having been, shall we say, ‘more than happy’ to kiss my printing career goodbye, I nevertheless have retained a love of old books over the years, with a particular interest in how paper was produced, the printing styles and techniques used. As I gazed over one volume in particular, my mental brakes were slammed on and I had a…’what the’… moment. What caught my eye was a fly. Or gnat or baby mosquito, what ever it was, it was squashed into the page. My first thought, naturally, as a trainee-semi-professional type was to decide if it was recent. Judging by the colouration and lack of imprint of the mini-beastie on the opposite page, it had been there for some time. ( I should mention at this point, my second thought, was ‘Oooh… Jurassic Park! Let’s clone a 17th century person from the dna!’) I would like to think that it is historic, as a 300 year old gnat flying too close while the paper was in production is a bit more of a romantic notion, than a 21st bug too daft to get out of the way the last time the book was shut…

Book worms are devastating little critters and thankfully, the only evidence I found had been there for sometime. There was no indication the holes were fresh and no ‘frass’. This is a powdery deposit left behind by munchers. But this was no ordinary pattern of devastation. This looked suspiciously like a ‘Rorschach ink blot’, and my instant mental description of the image was a turtle but from another page looked like a juggling beetle. Apologies for my overactive imagination but as they say in downtown LA, ‘that’s how I roll’…