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

[Richard Knoppow]

----- Original Message ----- 
From: "Earl Johnson" <earlj at comcast.net>
To: "The alternative photographic processes mailing list" 
<alt-photo-process-list at lists.altphotolist.org>
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 
alternative printing process.


--
Richard Knoppow
Los Angeles
WB6KBL
dickburk at ix.netcom.com