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

[C.Breukel at lumc.nl]

If you want the maximum yield of UV energy through glass one should buy Quartz glass, it will pass the lower (more energetic and thus dangerous) wavelengths of UV. Quartz cuvettes are used in spectrophotometers to measure wavelengths below 350nm (I believe it's 350, have to look that up). I once had a small 4*5 printing frame with a piece of quartz glass, cannot remember if I had really shorter printing times

Now I think of it, the UV tubes are made of glass, so the lower wavelengths are not emitted anyway..

Oh I guess quartz glass is prohibitively expensives, I could pick up a large broken plate for free..

Best,

Cor

> -----Original Message-----
> From: alt-photo-process-list-bounces at lists.altphotolist.org [mailto:alt-
> photo-process-list-bounces at lists.altphotolist.org] On Behalf Of Johnny
> Brian
> Sent: maandag 30 januari 2012 0:03
> To: py1hy at terra.com.br; The alternative photographic processes mailing
> list
> Subject: [alt-photo] Re: repairing scratch in the glass over the vacuum
> frame
> 
> Lead makes glass yellow. Lead (as in leaded crystal) was added so ordinary
> blue-green soda-lime glass would appear colorless. Glass with significant
> lead content (to block x-rays) is perceptibly yellow. I think float glass
> today is made on molten tin.
> Johnny Brian
> On Jan 29, 2012, at 2:02 PM, Jacques Augustowski wrote:
> 
> >
> > 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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