Distinguishing Bank Note stamps printed on "white wove paper" from those printed on "soft porous paper".
Howard M. Relles
rellesh@yahoo.com

    An effort to unambiguously distinguish Bank Note stamps printed on "white wove paper" from those printed on "soft porous paper" is underway.  It is based on the known phenomenon that soft porous paper will wick water faster than hard paper.
    Used Bank Note stamps, generously loaned to me by Dr. Charles Di Como (USPCS secretary and board member) and David Medeiros (owner of Quality Stamps of Venice, FL), were completely freed of all remnants of hinges or residual gum (from hinges) in warm (about 130F) water.  After drying them flat between clean paper (with only the weight of one sheet of paper on top) and allowing them to remain at 80°F (60% relative humidity) for at least 6 hours, a 3.5-4.5mm drop of water was carefully placed on the back of each stamp on a horizontal surface (on a hard white paper) and allowed to form its mostly circular wicking pattern.  The maximum wicking distance (the largest diameter of the mostly circular wicking pattern) was measured in millimeters after 5 minutes.  The wicking results are listed below (in mm/min.):

Wicking (mm/min.) for BANK NOTE STAMPS

Test
Stamp
 Partial
Description
 Wicking
mm/min.
 Stamp I.D.
(Scott #)
 Not This Stamp
(Scott #)
1-CD
 3¢ Washington, grill, no secret mark, tested Off grill
3¢ Washington, grill, no secret mark, tested On grill
 0.0
0.1
 #136

 ---
2-DM
 3¢ Washington, grill, no secret mark, tested Off grill
3¢ Washington, grill, no secret mark, tested On grill
 0.1
0.5
 #136
 ---
3-DM
 3¢ Washington, grill, no secret mark, tested Off grill
3¢ Washington, grill, no secret mark, tested On grill 		0.2
1.2
 #136
 ---
4-DM
 3¢ Washington, grill, no secret mark, tested Off grill
3¢ Washington, grill, no secret mark, tested On grill
3¢ Washington, grill, no secret mark, tested over 4 pinholes
 0.4
0.3
0.3
 #136
 ---
5-DM
 3¢ Washington, no grill, no secret mark
 0.0
 #147
 ---
6-DM
 3¢ Washington, no grill, no secret mark 0.0
 #147
 ---
7-DM
 3¢ Washington, no grill, no secret mark 0.0
 #147
 ---
8-DM
 3¢ Washington, no grill, no secret mark 0.0
 #147
 ---
9-DM
 3¢ Washington, no grill, no secret mark, opposite no cancel
3¢ Washington, no grill, no secret mark, opposite heavy cancel
 0.2
0.3*
 #147
 ---
10-DM
 3¢ Washington, no grill, no secret mark 0.4
 #147
 ---
11-DM
 3¢ Washington, no grill, no secret mark 0.5
 #147
 ---
12-CD
 3¢ Washington, no grill, secret mark 0.0
 #158
 #184
13-DM
 3¢ Washington, no grill, secret mark 0.0
 #158
 #184
14-DM
 3¢ Washington, no grill, secret mark 0.0
 #158
 #184
15-CD
 3¢ Washington, no grill, secret mark 0.3
 #158
 #184
16-DM
 3¢ Washington, no grill, secret mark 0.4
 #158
 #184
17-CD
 3¢ Washington, no grill, secret mark
3¢ Washington, no grill, secret mark, across flattened fold
 0.5
0.8
 #158
 #184
18-CD
 3¢ Washington, no grill, secret mark 0.6
 #158
 #184
19-DM
 3¢ Washington, no grill, secret mark 0.7
 #158
 #184
20-DM
 3¢ Washington, no grill, secret mark, opposite no cancel
3¢ Washington, no grill, secret mark, opposite heavy cancel
3¢ Washington, no grill, secret mark, opposite heavy cancel
3¢ Washington, no grill, secret mark, opposite heavy cancel
 0.8
1.3*
1.3*
1.4*
 #158
 #184
21-DM
 3¢ Washington, no grill, secret mark 2.1
 #184
 #158
22-CD
 3¢ Washington, no grill, secret mark 2.2
 #184
 #158
23-CD
 3¢ Washington, no grill, secret mark 2.4
 #184
 #158
24-DM
 3¢ Washington, no grill, secret mark 2.7
 #184
 #158
25-DM
 3¢ Washington, no grill, secret mark 3.0
 #184
 #158
26-DM
 3¢ Washington, no grill, secret mark >3.2
 #184
 #158
27-CD
 3¢ Washington, no grill, secret mark 3.4
 #184
 #158
28-DM
 3¢ Washington, no grill, secret mark, across thin area >4.0
 #184
 #158
29-DM
 3¢ Washington, re-engraved
3¢ Washington, re-engraved
 1.8
1.6
 #207
 ---
30-DM
 3¢ Washington, re-engraved
3¢ Washington, re-engraved
3¢ Washington, re-engraved
 2.6
2.1
2.4
 #207
 ---
31-DM
 3¢ Washington, re-engraved
3¢ Washington, re-engraved
 2.6
2.5
 #207
 ---
32-DM
 3¢ Washington, re-engraved >2.6
 #207
 ---
*Heavy cancel opposite where the drop was placed seems to increase the mm/min. of wicking.
Discussion:
In the case of the 3¢ Washington Bank Note issues, it is of course not necessary to define the paper in order to tell which are the #136's (with grills), the #147's (no grill, no secret mark), and the #207's (no grill, re-engraved).  However, this is exactly what is needed in order to tell #158's from #184's.
This effort is continuing.