a) Freshly mixed potassium dichromate in the % solutions indicates was =
used as the sensitizer.
b) The same batch of carbon tissue was used for
all tests. This was a warm brown tissue made=20
from 3 parts Carmine Crimson, 4 parts Brown, 3
parts Primary Yellow, and 2 parts Sumi Ink=20
concentrate.
c) Exposure was to a #2 Kodak step tablet.
For exposure the tissue was placed 4 inches=20
from the light source, in a bank of tubes=20
separated from each other by about 1/4 inch.
Tests were made with all UV tubes (UV), a
combination of UV and Cool White tubes=20
(Comb) or all Cool White tubes (White).
d) Exposure was 20 minutes, in all cases enough =09
to produce two steps of maximum density.
e) Tissue was kept in contact with final support=20
for 10 minutes, and warm-water wash-off=20
(development) was for 6 minutes at 107F.
f) Test strips were cleared in a 3% sodium=20
bisulfite solution.
f) Density readings were made with an X-Rite=20
reflection densitometer.
Test One (Comparison of Sylvania UV tubes and GE Cool White tubes at sens=
itizer strength of 1% and 1/2%. *My experience with 350na tubes in carbon=
printing is that they are very sensitive but produce images very low in =
contrast unless used with very dilute dichromate solutions, which of cour=
se in turn lengthen exposures somewhat.
sden 1/4% 1% =09
UV Comb. White UV Comb. White
1. 1.73 1.44 1.38 1.30 1.48 1.40
2. 1.67 1.40 1.32 1.26 1.44 1.34
3. 1.52 1.31 1.21 1.22 1.38 1.27
4. 1.49 1.29 1.07 1.17 1.28 1.24
5. 1.40 1.23 .96 1.14 1.18 1.13
6. 1.32 1.06 .81 1.07 1.14 1.05
7. 1.21 .96 .59 1.06 1.10 .88
8. 1.13 .84 .37 1.00 1.05 .74
9. .99 .63 .13 .90 .93 .49
10. .81 .49 .11 .81 .85 .19
11. .65 .31 .08 .71 .76 .14
12. .49 .13 -- .66 .67 --
13. .29 .11 -- .62 .53 --
14. .15 -- -- .57 .44 --
15. .05 -- -- .38 .35 --
16. -- -- -- .36 .27 --
17. -- -- -- .16 .12 --
18. -- -- -- .11 .10 --
19. -- -- -- .08 .08 --
Test Two (Expose with Cool White Tubes alone, sensitized with 2%, 3% and =
5% potassium dichromate. Exposure for 20 minutes). Compare UV exposure wi=
th 1/4% sensitizer with Cool White exposure at 5%!!!
sden 2% PD 3% PD 5% PD
1. 1.58 1.60 1.76
2. 1.55 1.56 1.73
3. 1.46 1.44 1.65
4. 1.29 1.39 1.46
5. 1.22 1.24 1.36
6. 1.09 1.17 1.28
7. .93 1.02 1.16
8. .78 .95 1.04
9. .62 .86 .93
10. .42 .68 .81
11. .34 .62 .68
12. .29 .54 .61
13. .20 .26 .56
14. .13 .20 .34
15. .10 .12 .16
16. .08 .08 .13
17. -- -- .08
18. -- -- --
=09
=09
My conclusion:
1) When the dichromate sensitizing solution is adjusted to the exposing l=
ight the Cool White tubes are as effective in exposing carbon tissue as 3=
50na UV tubes.=20
The characteristic curve plotted from tissue sensitized with a 1/4% potas=
sium dichromate solution and exposed with 350na UV tubes is virtually ide=
ntical to that plotted from tissue sensitized with a 5% potassium dichrom=
ate solution and exposed with Cool White tubes. The results from my plott=
ing are:
UV (1/4%) Cool White (5%)
Dmax 1.56 1.59
Dmin .09 .11
DR 1.47 1.48
Av.Grad .88 .77
ES 1.68 1.91
Sp Pt 0.65 0.67
I would surmise that had the tissue exposed to the cool white tubes been =
sensitized at 4% the results would have been even closer in terms of the =
Av. Grad and the ES.=20
2) When the tissue is sensitized with dichromate solutions of 1% or more =
there is a strong suggestion that a combination of UV and Cool White tube=
s is more effective than either along. I have conducted some further test=
s to confirm this but don=D5t want to bore you with any more details for =
now. I base this observation in part on my belief that more even results =
are obtained in carbon printing when the strength of the dichromate sensi=
tizer is 1% or stronger.=20
Anyway, I welcome your comments and suggestions about these tests. Now I =
gotta go make some prints.