[alt-photo] Re: repairing scratch in the glass over the vacuum frame

[Jacques Augustowski]

 Look at the glass sideways if it is green the more lead it has, all
architectural glass is green. The bluish color in more expensive glass
means that it has less lead and it is said that it is best for
transmitting UV rays. Float glass has both surfaces perfectly parallel
 ,  that means that this glass is optically good.  They call them
float glass because when the glass pane comes out of the furnace in a
molten state it cools down on the surface of molten lead. The green
glass also attenuates more IR rays than the bluer glass. 
 Jacques Augustowski 
             PY1HY 
 On Dom 29/01/12 15:36 , Nelson Mark ender100 at aol.com sent:
 I used 1/4 " plate glass and had the corners rounded and all the
edges ground with a slight rounding.
 On Jan 29, 2012, at 10:52 AM, Richard Knoppow wrote:
 > 
 > ----- Original Message ----- From: "Earl Johnson" 
 > To: "The alternative photographic processes mailing list" 
 > Sent: Saturday, January 28, 2012 9:58 PM
 > Subject: [alt-photo] Re: repairing scratch in the glass over the
vacuum frame
 > 
 > 
 >> I have replaced the glass on both sides of my flip top Nuarc with
Ace Hardware window glass with no apparent decrease in exposure times.
On my unit, the glass is held in place by screws that are easily
removed with the correct Allen wrench (hex key).
 >> 
 >> Earl Johnson
 > 
 >    My only experience with this was replacing the missing glass top
on a military contact printer (forgot the name) which uses a group of
argon lamps as the source. I made a crude measurement of the UV
transmission by looking at the fluorescense of the brightening dye
used in paper. I used thin plate glass, it was obvious that the glass
attenuated the UV significantly. The printer also has a diffusion
glass, the original was cracked but servicable after repairing with
optical cement. That has no noticable UV attenuation. The glass I got
for the top is green when looking at the edges, the diffusion glass is
clear. I did not attempt to find glass with good UV transmission
although I think such glass is available for special uses such as
green houses. The UV transmission is sufficient for normal
silver-gelatin contact paper. There were no bits of the original left
so I don't know what its characteristics are. I doubt if this printer
is intense enough for use in any POP alterna
  tive printing process.
 > 
 > 
 > --
 > Richard Knoppow
 > Los Angeles
 > WB6KBL
 > dickburk at ix.netcom.com [2] 
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