[AussieLad]

So i am all set to start printing this weekend (first attempt at doing a step wedge test to determine exposure times), and then i read a thread about someone having trouble exposing possibly because the galss they are using has some sort of uv filtering properties.

The thread mentions that when looking at the glass edge, it may look sort of green. ^$&@#&. Mine looks green.

How big of an issue is it going to be? Its about 5ml thick, and i am only exposing with a 500w halogen.

I am encountering problems finding glass that doesnt have these properties. Anyone in australia with tips where to find decent unfiltered glass. I would assume most picture frames, windows, etc would have this stuff. I have looked on ebay and seen tempered glass for table tops. Does anyone know if the tempered glass would work?

Any advice is appreciated.

 

[PhilR]

So i am all set to start printing this weekend (first attempt at doing a step wedge test to determine exposure times), and then i read a thread about someone having trouble exposing possibly because the galss they are using has some sort of uv filtering properties.

The thread mentions that when looking at the glass edge, it may look sort of green. ^$&@#&. Mine looks green.

How big of an issue is it going to be? Its about 5ml thick, and i am only exposing with a 500w halogen.

I am encountering problems finding glass that doesnt have these properties. Anyone in australia with tips where to find decent unfiltered glass. I would assume most picture frames, windows, etc would have this stuff. I have looked on ebay and seen tempered glass for table tops. Does anyone know if the tempered glass would work?

Any advice is appreciated.

I've used glass with green edges without issues. It just indicates a higher iron content which is common in cheaper float glass. I used toughened glass in my exposure unit white has much less colouration but I guess you need higher quality glass for the tempering process.

 

[Rodney]

:: edited thread TITLE to be more descriptive ::
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[ScreenFoo]

Just about anything has UV filtering properties--even the expensive low iron glass will still filter a bit of UV from your light source.

I wouldn't put low iron glass at the top of the list as far as an exposure set up goes--I'd take a good vacuum pump and blanket over good glass for improving exposures any day--assuming you don't have scratches or inclusions in the glass.

I'm building a new exposure frame, and I called 8 places out of the phone book--most of them treated me as some sort of loony or alien--one guy said he could get it. And it runs 4-5 times more money than the standard iron content stuff. I believe it's more common in the greenhouses, since the plants need that UV, as well as "thermal" glass for skylights that heat houses--perhaps it will help you on leads. It may be one of those things you really need to track down if you want it.

Phil: From what I've learned, tempering (I'm guessing that's the equivalent to "toughening"?) doesn't really change anything about the UV transmission, just makes it stronger, more heat resistant, and ensures that if it breaks, it breaks into tiny pieces instead of huge shards.

 

[AussieLad]

Well, i've decided just to give it a go with the glass i have and see what happens. The glass companies i have asked couldnt be bothered replying to my questions.

Really wanted to eliminate as many possible problems as i could before i start, but its time to take the plunge.

Thanks

 

[PositiveDave]

Just put the glass over half the screen and see if there's a big difference in the washout. That will tell you if it's been uv treated.

 

[PhilR]

Phil: From what I've learned, tempering (I'm guessing that's the equivalent to "toughening"?) doesn't really change anything about the UV transmission, just makes it stronger, more heat resistant, and ensures that if it breaks, it breaks into tiny pieces instead of huge shards.

Yeah, I figured the glass would need a purer composition to withstand the tempering process is all. Toughened glass is crazy stuff, the process leaves it with an outer "skin" that is under much higher tension relative to the core. It'll take a lot of abuse but if it gets even a tiny scratch it'll likely just implode as all the tension comes unreavelled. I spent some time working in a shop once and we were throwing out a bunch of display shelves. We couldn't break them no matter how much heavy crap we dropped on them. Then one of the other guys carried some from the warm shop to the freezing air ourside and it just exploded in his hands! We laughed, he didn't.

Slightly off-topic there.

 

[ScreenFoo]

I know you can get low iron glass tempered, I was thinking I should have asked the glass guy if there was some huge difference in price on that too.

One of the guys I used to work with tried to cut a piece for the exposure unit and didn't do it quite right--it was pretty fun watching it self destruct just sitting on a counter. Took like three minutes.

 

[DanAxe]

As stated by the previous person posting, most glass has some type of greenish hue when viewed from the edge so that is not how to detemine if the glass is "clear" or not. What you were being warned against is glass that has a film laminated to the glass, or between 2 layers of glass. This is sometimes referred to as Saftey Glass...the film holds the pieces of glass together should the glass break...while that is great from a breakage perspective, it can filter the UV light and increase exposure times. There are also hundreds of other glass formulas out there designed to serve many purposes, (including window glass that repels UV rays to keep your home cool) So when choosing Glass for your exposure unit just buy Standard Clear Float, it may have a green hue to it....it's Ok to have it tempered to add strength but that's all you need, this should be the least expensive glass in your Glass companies catalog.