Moisture Free Glass

[5th corner]

Hi Just had a customer request moisture free glass. I guess they are worried about their original art going mouldy? Any ideas. I have heard that perspex or I think you call it plexi glass has a lower dew point so less moisture. Anyway interesting question. Am seeking further clarifiacation of client thru decorator?

 

[preservator]

Condensation

Acrylic will be a less likely source of condensation, since it is a thremal insulator, while glass is a thermal reservoir.



Hugh

 

[Bob Doyle]

And reservoirs do hold water......

Does water white glass hold more water?

Probably had some pictures stick to their glass because of condensation, so now they want to avoid that happening again. You should talk to them about matting their photos for better protection.

 

[Jim Miller]

Does water white glass hold more water?

That's a good joke, Bob.

Actually, there may be dribble of accuracy in what you said. Water-white glass is generally 2 mm thick. The non-water-white picture framing glass used by most framers in the USA is 2.5 mm thick. One may presume that 25% thicker glass would require 25% more time for the permeation of heat, which would slightly (very slightly) reduce its propensity to condense moisture.

The permeation of heat through either thickness would happen quickly enough to reach dew point and condense moisture when the frame experiences a rapid radical change of temperature when humidity is present, which is why glass is called a poor thermal insulator.

Acrylic would be a much better choice than glass when dew point is a concern, such as in Direct Contact Overlay (DCO) framing. In addition to being somewhat thicker in framing applications, acrylic is made of plastic, so it slows the permeation of heat better than glass does, which is why it is called a better thermal insulator. By the time heat permeates the acrylic, the temperature inside the frame has begun to acclimate, which reduces the temperature differential enough to avoid the dew point more often.

 

[Bob Doyle]

If the humidity in the workroom was greatly reduced and then the glazing was sealed to the framing package would it be air and water tight? Would that reduce the changes due to the micro-climate the frame produces?

 

[Jim Miller]

If the humidity in the workroom was greatly reduced and then the glazing was sealed to the framing package would it be air and water tight? Would that reduce the changes due to the micro-climate the frame produces?

Yes, as shown in a dew point chart, lower humidity requires a larger temperature differential in order to reach the dew point. So, lower moisture content inside the frame would reduce the likelihood of reaching the dew point.

Drying the hygroscopic (porous) framing materials before fitting would reduce moisture content inside a sealed frame. Place the boards, etc. in a heated dry mount press for a while. You could also add a desiccant to regulate humidity. Trouble is, guesswork is involved, since most framers have no way to accurately gauge the moisture content of the materials. There would be no indication of failed frame seals, which could lead to a false sense of security for consumers. Also, very low moisture could adversely affect some framed items. For these reasons, I would leave sealed framing to conservators who are qualified to do it.