Really Short Exposure Times Gum Printing

Hello -

Im a total newbie. Im following Christina Anderson's latest book on Gum Printing to a T. In my initial printings of 21 step wedge to get a feel for exposure times, it appears that my proper exposure should be just 45sec. Every book an online research says that ~5 min is usual. Im using 10% dichromate, 3% M Graham Quin. Rose in 14o pre-mixed Bostick&Sullivan gum. 1:1 gum/pigment to dichromate ratio, brushed on with a hake brush.

I built a uv exposure box. Its just a box with 10 bulbs of 20 watt T12 BL. The distance from light to print is 5 inches.

Is this just how it is going to be with my setup, or am i doing something wrong?

James

Your 200 watts of light at 5 inches is too intense.

Remove half the bulbs if you can do so while maintaining even illumination. That should double your exposure time.

Or make the box deeper, maybe 10 or even 20 inches. That will increase the exposure time.

You need to repeat the tests after any change in the light source coniguration.

I don't see any advantage to a really long exposure time.
Perhaps modern lamps have much higher output than lamps when the book was written.

- Leigh

Leigh B said:

Your 200 watts of light at 5 inches is too intense.

Remove half the bulbs if you can do so while maintaining even illumination. That should double your exposure time.

Or make the box deeper, maybe 10 or even 20 inches. That will increase the exposure time.

You need to repeat the tests after any change in the light source coniguration.

I don't see any advantage to a really long exposure time.
Perhaps modern lamps have much higher output than lamps when the book was written.

- Leigh

Click to expand...

Thanks - I figured that might be the case. I didn't want super long exposures, but i'd like to have a little wiggle room. I will give that a try

James

Are you using a digital negative of the step wedge? Depending on how you print out a digital negative, the density of the negative can be quite different. Try different printer settings to see what might be best for you. Also, if you use PK ink, the negative will be less dense that a MK ink negative.

Have you tried to make a print using the Stouffer step wedge? Do several timed test like 1 minute, 2, 4, 8 to see the results.

Bruce