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Walter Susor
White Crane
Username: wsus
Post Number: 1236
Registered: 08-2003
Posted From: adsl-75-7-6-98.dsl.pltn13.sbcglobal.net
| | Posted on Sunday, September 28, 2008 - 08:20 pm: | 
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Hi All,
The use of ultraviolet illumination can sometimes be a useful tool to locate ceramic repairs. Many, but not all, cements and filler materials will fluoresce in the visual spectrum when illuminated with an ultraviolet light source. In these cases repairs can be easily seen by scanning the object with a simple hand held UV light source in a darkened room. Photographing the result, however, can present a challenge. Here is the method that has worked for me.
I am using an old "prosumer" model Nikon Coolpix 5000 camera that has an overload of custom settings that makes it useless for vacation photography, but OK for carefully set up photos using a tripod.
The UV source that was used is an old hand held lamp that is used for the identification of mineral specimens among other uses. My lamp is fitted with a filter to isolate 340 mu wavelength UV light that I had used for an analytical test many years ago. This additional filter should not be necessary. It will increase the required exposure time by reducing the light output of the lamp but blocks the small visual light output from the lamp that might overwhelm the fluorescence.
The intensity of the fluorescence is very low. The eye can readily adjust to the low light, but it is usually at the exposure limits of the camera. The room must be pitch black. A photography darkroom is ideal, but I use a darkened room away from street lights with the door closed. Even moonlight will overwhelm faint fluorescence. The maximum auto exposure on my camera is 8 seconds at f2.8. It was just adequate for the example shown below. Other cameras or longer exposure times with my camera will require use of the bulb setting and a guess to arrive at the proper exposure (or a darkroom timer). With the long exposure times, the lamp can be moved around to evenly illuminate a larger object.
To get a sharper, more focused image it may be necessary to use the fixed focus feature that is on many cameras. I think that the auto focus may not work under these conditions.
 
Best Regards, Walter |
Gerard Lin Y C
Golden Pheasant
Username: gerardly
Post Number: 821
Registered: 09-2005
Posted From: 220.255.7.135
| | Posted on Thursday, October 02, 2008 - 02:20 am: |
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Dear Walter,
Good idea. I have a "Wood's Lamp" somewhere around and I will try toying around with it.
Regards, Gerard. |
Gerard Lin Y C
Golden Pheasant
Username: gerardly
Post Number: 832
Registered: 09-2005
Posted From: 220.255.7.145
| | Posted on Friday, October 24, 2008 - 11:30 am: |
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Dear Walter,
Just an update. The UV light does little for Mid-Late Qing items (my collection) as most restorations can be seen by the naked eye. Nothing lights up for Qing items.
Regards, Gerard. |
Giovanni Repetti
White Crane
Username: grepetti
Post Number: 2781
Registered: 12-2003
Posted From: host203-41-dynamic.8-79-r.retail.telecomitalia.it
| | Posted on Friday, October 24, 2008 - 04:05 pm: |
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Dear Walter,
somehow I missed this your thread. There are also stronger UV lamp available if one is planning an intense use. Below is my Osram UV lamp, 125 Watt power. It is strictly recommended to avoid to look at UV light with naked eye, a common eyeglass is enough to filter the radiation.
Dear Gerard, what you say is very strange. What UV radiation is revealing is the difference of the nature of substance, the original one and the added one by the restoration. In old oil paintings this is very evident; I don't know if the materials used in ceramic restoration does not show a so great difference, maybe our friend Ricardo knows this.
Giovanni
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Gerard Lin Y C
Golden Pheasant
Username: gerardly
Post Number: 833
Registered: 09-2005
Posted From: 220.255.7.187
| | Posted on Friday, October 24, 2008 - 04:41 pm: |
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Dear Giovanni,
Apologies for not being clear.
Sure, UV light will illuminate different components differently.
UV light is very useful in detecting restorations in oil paintings.
But for Mid-Qing porcelain onwards, I reckon you can detect restorations with the naked eye, so the use of the UV lamp is not too useful.
Your UV lamp looks very powerful.
Regards, Gerard. |
Ricardo Manta Simões
Peacock
Username: ricardo
Post Number: 551
Registered: 06-2003
Posted From: 87-196-89-120.net.novis.pt
| | Posted on Saturday, October 25, 2008 - 11:51 am: |
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Hello Giovanni, all
I never needed to use this lighting source to identify restorations. What I know is that the fluorescence of materials under uv light differs from material to material mainly from inorganic to organic (from which restorations are made) materials.
"But for Mid-Qing porcelain onwards, I reckon you can detect restorations with the naked eye, so the use of the UV lamp is not too useful."
Don't be so sure Gerard.
Best regards,
Ricardo |
Giovanni Repetti
White Crane
Username: grepetti
Post Number: 2783
Registered: 12-2003
Posted From: host116-45-dynamic.3-87-r.retail.telecomitalia.it
| | Posted on Saturday, October 25, 2008 - 04:14 pm: |
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Dear Gerard,
sorry the fault is mine, due to my bad english.
Yes Ricardo, the main difference is from inorganic to organic, and this is the reason for it being useful in painting inspection.
Kind regards
Giovanni |
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