Friday, January 14, 2011

The visible light is so bright....I gotta wear shades (or tinted Plexiglas or fiber mesh screens, or...)

And here I thought tinting glass was just for the cars of male teenagers and diplomatic envoys - turns out I was mistaken. Apparently tinted windows are all the rage in the museum world. I found out more than I ever wanted to know about light filtration options for windows this past week.


But I’m confusing you – let me start from the beginning. I talked with the Hammer last week for updates on the progress of the restoration work. He has been working on shoring up the south side of the house – C channels, needle beams are in, most of nogging is out. Hey (Jude) was expected on site to take pictures of the exposed sill to share them with the architectural team so that they can make a determination about what type of sill and post repair is most appropriate. Until the architectural team makes that determination, no sill or post work can be done. Hey (Jude) was also supposed to bring a storm window mock-up for the architects’ approval as well.

View of the South Parlor - site of the next phase of structural work.


Scaffolding in place, check!

C-beams and needle beams in place, check!


Exposed sill in need of some type of repair or replacement the extent of which is not known at this point, check!
 I figured – ‘Whew! This is going to be a short and sweet blog this week!’ Had I talked with The Hammer alone it would have been, and I would have remained blissfully ignorant of The Great Glass Dilemma of ’11. However the Curator accompanied me on my fact-finding mission and when The Hammer mentioned storm windows, she began to ask questions. The questions revolved around the advisability of tinting windows. But the bigger story is UV A, UV B and visible light. I’m well aware of UVA and UVB – they are the reasons that when at the beach I slather on the SPF 107 sunscreen, wear a sweat suit under my bathing suit, and make my children walk around in their snowsuits while they build castles in the sand. Visible light – not as afraid of, mostly because it allows me to see. But visible light is not the innocent little range of electromagnetic radiation that can be detected by the human eye it tries to make itself out to be. While it is true UV A and UV B light causes degradation of material, visible light does its fair share of damage – it fades things.

According to the Curator because we do not need UVA or UVB light to see it can be eliminated almost entirely (hence the SPF 107 and the sweat suit under my bathing suit – my family thinks it’s overkill, I think it is a safe way to enjoy the sun). However we need visible light because without it we can’t see. The museum’s goal then is to reduce the amount of visible light that enters through the windows into the house to the minimum levels necessary to see. The good news is that it seems like any glass will block UV B radiation while applied filters will block UV A. But what to do about that pesky visible light?

Well, what are the options? Aaaah…ha ha – if only that were an easy question to answer. One option is to apply a tint to the exterior glazing of the window to filter out visible light. The percentage of visible light filtration you want dictates the amount of tinting necessary. And don’t think there is only one tinting option out there for glass – there are more, for example, bronze tinting or gray tinting – and I have no idea what either of those two things would look like. Tinted glazing for controlling visible light is usually done in the museum world on interior storms made out of Plexiglas. But the museum is not mounting interior storms, it is mounting exterior storms. And regular glass will not be used in the exterior storm windows – instead the exterior storms will be made with safety glass. The reasoning behind this is simple – we want to protect the historic fabric of the house that we are currently spending mucho dinero to restore. In other words we don’t want a thousand black birds to fall from the sky dead and have a portion of those dead black birds crash through our windows damaging any of the historic material of the house. (Actually we don’t want a thousand black birds falling dead from the sky period – that’s a little too end-of-times for me) Safety glass will break but it won’t shatter all over the place. Besides, the Plexiglas is easily scratched – that’s okay when it’s on the inside, but it would start to look pretty bad on the outside what with its exposure to dead birds falling from the sky, etc.

Darn those Mayans and their calendar!

One of our concerns with tinted exterior storms is the way the house will look with all of that visible light reflecting back off. Sunglasses can make movie stars look cool, or State Troopers look intimidating, but in the case of Cherry Hill it will only succeed in blinding anybody who looks at the house on a bright, sunny day. Rule number one in the Dummies Guide to Historic House Museum Interactions with the Public – do not blind the public. The Curator did wonder if there was an option of applying an anti-reflective coating to exterior tinted storm windows that would reduce the amount of reflection/potential blinding of passerby.

Long after the interrogation of Joe the Hammer had ended, the glass discussion carried on (and on…and on, I’m not kidding – like for the rest of the week). The Director and the Curator mentioned that there are fiber mesh shades that can be mounted on the interior of the window to reduce visible light. Actually, in the interest of full disclosure and since this is supposed to be a helpful and informative blog, the Curator and the Director used their “official” name for these shades: “screeney blinds.” The plus of the “screeney blinds” is that they will block visible light in a non-permanent way; the negative is that they provide a less clear view out of the window they are mounted on. Some staff members (the Curator) were open to the idea of exploring the option, other staff members (the Director) were vehemently opposed and then there were the staff members (the Communications Coordinator) who were stumped over how to spell “screeney” - (“Do I put the third ‘e’ in or do I leave it out?”).

The other option is to continue the method currently in use at the house - blackout shades and UV shades that staff members have to remember to raise for a tour and then lower after tours are over. A little more manual effort certainly but it does the job, once again in a non-permanent way.

Just when we thought we would continue to wander in a forest of UV and visible light uncertainty we found enlightenment. The Curator contacted The Light Guru. The Light Guru answered her questions and gave her a sense of calm where before there had been only a tinting tizzy. The Light Guru is a private conservator who happened to design the HVAC system for the museum’s collections center. The Light Guru explained that the tinting levels we would need might not be available in laminated glass. He explained that if we wanted to go the tinted route that we should get Plexiglas tinted to whatever percentage of filtration we wanted and install that between the historic glass and the exterior storm – the thought being that the exterior windows might look better this way. He suggested that the museum measure the light levels of the windows using a footcandle sensor device or a light meter. (Light is measured in footcandles or lux.) Once we know what amounts of visible light we are dealing with, we will be able to make a better informed decision.

But not to be outdone by the Curator’s window nirvana, the Director pulled a card from up her sleeve and contacted another conservator who has worked with the museum before, via a mini-teleconference (in the interest of protecting her privacy we will refer to her as the Conservator Extraordinaire). The Conservator Extraordinaire actually suggested we contact The Light Guru in the first place and when we talked with her after The Light Guru’s enlightenment, she gave us some food for thought – she suggested the use of tinted Plexiglas on the interior which would lower the amount of light coming in the window, make window treatments last a lot longer and prevent an Apocalypse Now (unless you are a black bird in Arkansas) if a staff member happens to forget to shut any of the blinds or shutters. It is an option of continuous protection that takes the manual labor associated with the UV and blackout shades option out of the equation, and lowers the baseline of visible light that enters a given window.

The Curator, whiz kid that she is, is currently thinking about a different approach to visible light management. The museum could use pull-down blackout shades when it is not open, and when it is open to tours (an optimal time to let visitors have some visible light so they can appreciate their surroundings) the blackout shade would be fully raised. But what about the visible light and the UV A light?!?! Never fear – in addition to the blackout shade would be a fully closed semi-translucent shade which would allow light to enter the room more evenly but in a reduced amount. The museum would use reproduced historic window treatments or adaptations of them for further reduction of light. But just to complicate what seems like a simple straight forward method to deal with visible light, the Curator will explore different options in different rooms of the house. Perhaps in one room, like our Guest Bedroom where the view out the window is part of the tour – maybe tinted Plexiglas would be installed there. All those light measurements The Light Guru suggested will come in handy making these decisions.

After all of the talking and after the advice of the conservators, it became painfully clear to the Director and the Curator what needed to be done……..Road Trip!!! Obviously in order to make the most informed decision possible, in addition to light measurements and advice from the experts, we need to see how these different options look in the real world, or at least the real world of historic house museums. And we also need to buy some snacks for the road. I’m thinking Slim Jims and Cheetos. But no coffee – can you imagine how many bathroom breaks the Director and Curator would have to take on a road trip where they were given coffee in the car? To this end the Director and the Curator have set up some visits to sites this week to help with their research. I have been invited on the trip, and if weather and childcare conditions allow, I will go along for the ride. The only thing I have left to say is “SHOTGUN!” (Sorry Curator but it’s an unspoken rule of the road – whoever shouts SHOTGUN first gets the front passenger seat.)



***Updated Information – We have since found out that it is possible to get laminated glass that is tinted dark enough. The catch is that the extra layer of tinting to the laminated glass “sandwich” may not look well and it may end up being too thick to be physically feasible for the museum’s particular windows.***

No comments:

Post a Comment