Malde-Ware M2 50-50 Pt/Pd // Base Exposure Time // power light source and distance with contact print

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Dear All,

lamps

8 x 25 Watt (fluorescent tubes 450 mm) // Sylvania T8 BL368 18 Toughcoat™

Non dimmable and 4 electronic ballast are used for powering up the lamps.

set-up (as diffuse source)

IMG_1400
IMG_14002048×1536 451 KB

This gives +/- 0,16 Watt/cm2 (for the light source)

distance between light source (see above) and contactprint

IMG_1395 copy
IMG_1395 copy1449×1337 438 KB

+/- 170 mm

  • Did I understand well, as mentioned in Pradip and Mike’s book for Platinotype that with a ‘diffuse source’ the distance plays a more significant roll on the exposure if the distance is in steps of +/- 150 mm? (It seems in my set-up and lamps that after some tests (with 100 mm and 170 mm distance light source/contact print) there is no difference between 100 mm and 170 mm.)

The ‘problem’; to short Base Exposure Time

I’ve made test strips (Platine Arches 310 // Malde-Ware Method 2 50-50 Pt/Pd) to obtain the Base Expousre Time (Chapter 7 as per above mentioned book). I’ve used a glass rod aswell a humidity box.

The best results are the following:

IMG_1409
IMG_14091536×2048 904 KB

What gives me an exposure time of about 2 minutes. In my feeling/opinion to ‘short’ for this time of light source (fluorescent tubes).

  • Currently the distance between light source and contact print I can increase until +/- 200 mm.
  • I can replace the lamps with lamps of 15 Watt each (total of 120 Watt). This wil result in a power of +/- 0,09 Watt/cm2

Anye ideas/suggestions/comments?

Thanks.

Peter

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" * Did I understand well, as mentioned in Pradip and Mike’s book for Platinotype that with a ‘diffuse source’ the distance plays a more significant roll on the exposure if the distance is in steps of +/- 150 mm? (It seems in my set-up and lamps that after some tests (with 100 mm and 170 mm distance light source/contact print) there is no difference between 100 mm and 170 mm.)"
Hi Peter!
The opposite! :slight_smile: See page 61: “For a diffuse light source, exposure changes are almost insignificant
as adjustments of up to ca. 6” / 15 cm are made…"

Regarding exposure times: If you are achieving a full base exposure without banding (uneven distribution of the light source) with 2 minutes, great! There is no advantage to lengthy exposure times, unless you want slightly cooler print tones – see page 160, section on Exposure duration.

Also, from the above image of your tests, it seems you are not exposing with an overlay of film (UP OHP or processed photographic film with base+fog) … it is hard to see, so forgive me if I am wrong.

Hope this helps.
P