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 Post subject: Small Artifact Preservation Method Suggestions Needed
PostPosted: Thu Aug 08, 2013 10:42 am 

Joined: Sun Aug 22, 2004 8:28 am
Posts: 2435
Location: Salt Lake City, Utah
All,

As a going away present, a friend gave me the glass headlight side numberplate from Louisville & Nashville 1961, a 2-8-4 "Big Emma." He's owned it since the late 1950s when a friend who worked in a scrap yard in Cincinnati gave it to him, knowing he was interested in railroading. The plate survived his move to St. Louis in 1962, but at some point was cracked into about 5 pieces.

I'd like to display the item in my home, but was curious as to suggestions on how to do it. My initial idea is to "sandwich" it between two pieces of plexiglass/Lexan and build a frame around it. That way, you could view both sides of the numberplate, but the frame would hold it in one piece. I

'm also at some point going to make a tracing of the lettering to keep. I've attached a photo. Any alternate suggestions are welcome. It's a neat item and I'd like to stabilize it but also keep it where I can display it.


Attachments:
L&N1961Plate .jpg
L&N1961Plate .jpg [ 91.99 KiB | Viewed 1033 times ]

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David M. Wilkins

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 Post subject: Re: Small Artifact Preservation Method Suggestions Needed
PostPosted: Thu Aug 08, 2013 11:10 am 

Joined: Tue Aug 31, 2004 3:04 pm
Posts: 86
Location: San Jose, CA
Creating a frame to hold the pieces together and protecting against future damage is a good start; however, when applying the plexiglass sandwich, leave a gap between the plexi and the artifact. This will protect against potential chemical reactions between the plexi and the number board. A long term conservation goal is separating, when possible, any dissimilar materials. Additionally, the small gap will allow for some air flow of any outgassing that may occur.

Ken Middlebrook
Collections Manager
History San Jose


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 Post subject: Re: Small Artifact Preservation Method Suggestions Needed
PostPosted: Thu Aug 08, 2013 11:21 am 

Joined: Sun Aug 22, 2004 8:28 am
Posts: 2435
Location: Salt Lake City, Utah
Ken,

Thanks for the insight. If I used regular glass instead of the plexi, would I still need to do the air gap?

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 Post subject: Re: Small Artifact Preservation Method Suggestions Needed
PostPosted: Thu Aug 08, 2013 7:22 pm 

Joined: Tue Aug 31, 2004 3:04 pm
Posts: 86
Location: San Jose, CA
David,

Yes, as you want to limit the amount of direct touching of ANY artifact, including but not limited to documents, photographs and number boards. Matting within framed objects will provide the same protection of a gap away from the chosen protective shielding.

I have seen multiple cases of newly donated artifacts being literally stuck to the protective shielding. Artifact removal in these cases require considerable care without causing damage. Unless there is significance of the framing, we typically remove and rehouse the artifact using archival material.

Ken


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 Post subject: Re: Small Artifact Preservation Method Suggestions Needed
PostPosted: Thu Aug 08, 2013 9:12 pm 

Joined: Fri Aug 20, 2010 8:25 pm
Posts: 243
David,

Although Ken makes some very good points about not wanting to touch the surface of an artifact and allowing for things to outgas, and about dissimilar materials in contact what you have here is several pieces of glass with rough broken edges in contact.

Glass is a very funny material; once a fracture or crack starts it will slowly propagate until it runs out of material. Those rough broken edges will (if not restrained) rub back and forth against each other (due to thermal expansion and plain old vibrations) and possibly start more cracks. Those rough edges should be stabilized. At the very least you may want to consider taking a very smooth diamond coated stone and gently rounding the edges of the glass where the breaks are. Not enough to remove too much material, but you want a smooth rounded edge. Sharp 90 degree edges concentrate stress and may cause smaller cracks along the big broken boundaries.

I would not display those separate pieces of glass vertically (where the top pieces are pressing down on the lower pieces). Those rough edges will chip pieces off the lower parts eventually.

Options to consider;

1) Stabilize the separate pieces by bonding them back together with a UV curable optical cement (search on NORLAND optical adhesive). This is a clear cement that is index matched to the base glass and is nearly invisible if applied carefully. A modest expense, look at “Edmund Optics” where you could get the stuff for a job like this for a few hundred dollars.

2) Display the piece horizontally with the broken edges intentionally separated so they cannot rub against each other.

3) Maybe you could bond each piece of glass to a clear plastic sheet (polycarbonate) with three small dots of clear silicone RTV between the front (no paint) side of the glass and the plastic. You would still want to keep a space between those rough glass edges. The silicone would “give” a little bit to take care of the difference in size of the glass and polycarbonate when the temperature changes. Start by bonding one piece and letting the RTV cure, then bond another piece with a few small paper shims to keep the crack (break) separated. After everything has cured remove the paper shims.

3) You could bond the front side (surface without paint) to another thin glass sheet with the UV curable cement, this might be expensive but would give you a piece that could be displayed vertically with safety. The use of glass would make the thermal expansion the same for the artifact and the supporting glass substrate. The glass surface will not outgas anything and this would keep you from contacting the painted side. But this is very probably irreversible.

Of course it depends on your budget and if you want to enjoy the piece or preserve it as a future reference piece.

I do not work in the museum field, but I do work with glass pieces (lenses, mirrors, etc.) all the time. It’s a funny material, we have a saying, “there are two kinds of folks that work with glass; those that have broken some, and those that will break some”.

We have on occasion taken large glass pieces with cracks and drilled out the ends of the cracks (turns a pointed end of the crack into a circle which reduces the stress) to stop them from propagating and then filled the crack with a cement with similar thermal expansion characteristics, quite elaborate but it will stabilize a crack and stop it from getting bigger.

Cheers, Kevin


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 Post subject: Re: Small Artifact Preservation Method Suggestions Needed
PostPosted: Thu Aug 08, 2013 9:29 pm 

Joined: Fri Aug 20, 2010 8:25 pm
Posts: 243
David,

Just one other thing that I forgot to mention;

No matter how tempted you may be DO NOT EVER USE "SUPER GLUE" around glass. The curing process of the "super glues" (cyanoacralyte, not sure I spelled that right) will give off fumes that WILL FOG the glass.

Even when using the RTV's you will need a fan to remove the acetic acid fumes (smells like vinegar) from your work area.

Kevin


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 Post subject: Re: Small Artifact Preservation Method Suggestions Needed
PostPosted: Thu Aug 08, 2013 11:12 pm 

Joined: Sun Aug 22, 2004 8:28 am
Posts: 2435
Location: Salt Lake City, Utah
Kevin,

Thanks for the advice, it is well-taken. I've sent you a PM with some specific questions.

Thanks again, this has been very helpful.

David

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