Yet another UV Light Query

Howdy all, I have a small fluorescent setup that I made for doing pd/pt work but was recently reading about graphics industry plate burners and associated lights. I was wondering whether any one had any experience with Olec graphics lamps or the like? They sound like they would be very bright (1000w-1500w) and would print quite fast, any thoughts?

Cheers,
Allan

Allan Phoenix said:

Howdy all, I have a small fluorescent setup that I made for doing pd/pt work but was recently reading about graphics industry plate burners and associated lights. I was wondering whether any one had any experience with Olec graphics lamps or the like? They sound like they would be very bright (1000w-1500w) and would print quite fast, any thoughts?

Cheers,
Allan

Click to expand...

Olec graphic lights are high quality units, but with a 1000w-1500w unit your exposure times are not likely to be a lot faster than with your fluorescent unit. My NuArc 26-1K plateburner, which has a 1000 watt metal halide lamp, actually prints slower than my UV bank of BLB tubes.

Another thing to consider is that unless you also buy a light integrator to use with the Olec unit you will have to turn it on for about 2-3 minutes to warm up before beginning exposures. This may make it less convenient to use than the bank of UV tubes. If you buy the Olec I would definitley recommend getting a light integrator to use with it.

Sandy

THE MISSING UV LIGHT LINK

Allan,

Several years ago I started my quest into non-toxic photo-polymer photogravure and in the process did some research on contact printing with UV light sources. (I don't have my notes to hand but will make a concerted effort to find them over the next few days and post actual test data). I will however try to summarize my findings (as memory allows) as follows:

a) different bulb types emit varying amount of UV; (big duh...!)

b) an integrator is a useful tool for measuring UV output especially as bulbs heat up (duh...!)

keep reading we're getting to the good part.... :{D

HOWEVER THERE IS A MISSING LINK THAT IS ALMOST ALWAYS OVERLOOKED

c) the between the source and the receptor glass filters out UV light transmission; some bulbs such as street light have a secondary glass mantle for exactly this purpose.

>>> How does this matter to Alternate Process practioners ? <<<

Consider the glass that stands between your receptor (print/neg/pos) and the light source in your contact-printing frame. It is filtering out (BLOCKING) some of the UV light coming in; this may explain why people are getting different results with the same light source.

TO VERIFY THIS: take a reading with your light integrator below the glass and compare the reading above the glass. The reading below will always be lower, the question is by how much. If the ratio is large then simply replace the glass with a high UV efficiency glass.

THE SOLUTION: [PHOTOCOPIER GLASS -> WHY? read on] Photocopiers work on the principle that UV light is used to adjust the static charge on the printing drum. The white areas of the paper reflect a lot of UV that destroys the static charge and thus the toner is not attracted to that area resulting in a clear or white area. Conversely where black lines do not reflect UV light the static charge remains intact and picks up toner resulting in a black area. To ensure that UV light passes through the glass efficiently photocopier glass is specifically manufactured to allow high rates of UV transmission.

When I built my contact-printing frame I contacted several parts suppliers for photocopiers until I found one with surplus glass for non-current models that I bought at a reduced price (it's somewaht expensive). I think the size was odd something like 15x19.5 and I didn't attempt to cut the glass. Instead I built the frame around it. My exposure times (I use a 1000 watt Olite) were about 40% of the old 1920's frame that I was borrowing.

As a side comment it is worth noting that for photogravure and other printing methods that involve burning a matrix a single source light such as the Olite must be used instead of a multiple source such as rows of fluorescent tubes. The reason is that the matrix must be projected into the rector media as a cylinder (single source) instead of a cone (multiple source). A cone result with multiple sources because the source on one side partially cancels out the projection from the other side and vice versa. This is not desirable because when the amount of development reduces the depth of the matrix and with a cone the cross-section decreases with depth whereas the cross-section is constant with a cylinder.

Anyway that’s probably enough for you to chew on for the moment.

Hope this helps. -Terrance

Terrance,

There are other sources for high UV transmitting glass other than copier glass.

What people want to look for is 'low iron' glass. This glass is sometimes used as framing glass because it looks very clear, without the greenish tinge of normal glass. 'Water White' is one trademarked name, by Denglas.

My information searches in the past indicated that typical low iron glass has about 1/3 the UV blocking of normal (borosilicate) glass. The difference is not great in the final exposure time, so I wouldn't go out and replace all your glass unless you have a reason to, but if you do need to, you may think about getting low iron glass.

---Michael

Michael Mutmansky said:

Terrance,

There are other sources for high UV transmitting glass other than copier glass.

What people want to look for is 'low iron' glass. This glass is sometimes used as framing glass because it looks very clear, without the greenish tinge of normal glass. 'Water White' is one trademarked name, by Denglas.

My information searches in the past indicated that typical low iron glass has about 1/3 the UV blocking of normal (borosilicate) glass. The difference is not great in the final exposure time, so I wouldn't go out and replace all your glass unless you have a reason to, but if you do need to, you may think about getting low iron glass.

---Michael

Click to expand...

Another "low iron" glass that transmits a higher percentage of UV radiation than regular float glass is a brand called Starfire.

I have personally tested a number of speciality glasses with increased UV blocking, including Starfire and Denglas, and agree with Michael that the difference in exposure time is very small, at best about 1/4 to 1/3 of a stop when evaluating glass of the same thickness. In my own case I considered the pros and cons of replacing the plain float glass in my two UV exposure units with one of the speciality glasses, but eventually decided that the small increase in printing speed was simply not worth the time and expense of doing so.

Sandy King

Testing UV glass for efficiency

I have tried the "low iron" glass that transmits a higher percentage of UV called Starfire but in the end got better results and a much better price with photocopiers glass. Photocopier glass is not cheap to be sure but if you are not in a hurry and call around a bit you can pickup some discontinued or "new" old stock, the price is much more reasonable. Mine has a couple of mounting holes in it but I didn't bother cutting them out as the glass size allowed me to print 11x14 with plenty of margins (containing the mounting holes).

If you know of a printing company (almost non-existent now) or an organization such as a fine art intaglio print studio that has a light integrator and a UV plate burner you can take a small sample (1" x 1") of the glasses in question and place it directly over the integrator measuring cell and with the burner properly (consistently) warmed up, determine how much more effective the glasses are relative to one another. This data can help you make the determination if the cost of upgrading is worthwhile.

Perhaps the ultimate contact printing frame is the commercial printing vacuum frame setup that sits under a plate burner. High efficiency UV glass that is large and the vacuum keeps the paper flat. If you're lucky it will still have the matching burner and integrator as well and this will make printing a pleasure to do consistently. The down side is that this setup is quite big and heavy with a storage cabinet underneath with a compartment containing the vacuum pump (will it go down your basement stairs?). Somewhat expensive even at a fraction of the original price ($100s instead of $1000s) But if you've got the room you might find one languishing in some reclaimed equipment depot. Getting somewhat scare now as everyone has switched to digital.

sanking said:

In my own case I considered the pros and cons of replacing the plain float glass in my two UV exposure units with one of the speciality glasses, but eventually decided that the small increase in printing speed was simply not worth the time and expense of doing so.

Sandy King

Click to expand...

Another issue that I forgot to mention is the thickeness of the glass. Glass that is 1/16" thick transmits a much larger percentage of UV radiation than glass that is 3/8" thick. I have tested this with UV densitometer and the difference between glasss that is 1/16" thick and 3/8" thick and the difference is 1/2 to 2/3 of a stop.

As far as I understand, and I have spoken to people at both Olec and NuArc about this, the glass used in the vacuum frames of their platemakers and vacuum easels is plain float glass.

Sandy King

Check out this site. http://www.pgo-online.com/intl/jse/....html?Content=/intl/katalog/fused-silica.html

It has some interesting information about the UV transmission of various types of glasss. My reading of the various transmission charts suggests that in the range of 300-400 nm there is at maximum only about a 20% difference in transmission between clear white float glass and glasses with maximum UV transmission.

Sandy

A couple things. If the light unit doesn't have an integrator built in, you could use a Metrolux timer which is an external integrator which can be attached to any light source. I use Metrolux timers on my UV unit and my cold light heads for perfect repeatability. I don't know if they are still made, but if not you could probably find them for sale used. The Metrolux II is the better unit.

Also, if you do the test holding an integrator light-reading cell above and below the glass for comparison, make sure you know what UV bandwith the sensor is reading. If it reads a braod range of light, you're not getting a perfectly accurate reading of UV light loss since the UV light loss is proportional to the total light loss. As others have said, the difference is pretty small anyway, but the best bet comes in printing.

I am sure that Eric is on the list some place. Start looking for meteredlight.com for the web site. Both Karl and Eric do a great job on products. The timers are the best.

Jan Pietrzak