Also, thanks for the compliments.

This may seem ridiculous, but I find the effect is best accomplished via repetitive tweaking, trying to work with the elements that are unique to each photo. Here is the result of my layers, many of which involve painted brush strokes, either on the layer or a mask:

   1. Sharpen duplicate layer of original photo (Unsharp Mask or whatever method you prefer)
   2. Copy of Blue Channel, set to Linear Burn, Fill 25%; masked out darkest edges of photo
   3. Curves adjustment layer, masked to darken lighter regions of face
   4. With all layers off, other than the original photo, select > color range > highlights, fill with white, g-blur 3; set to Overlay, Fill 25% (afterwards, remember to turn all the other layers back on)
   5. Hue/Saturation adjustment layer [colorize checked] 30 50 -50; create clipping mask (Ctrl/Command-G)
   6. Hue/Saturation adjustment layer 0 -15 0; masked out lips
   7. Hue/Saturation adjustment layer [colorize checked] 50 25 0; Normal, Fill 25%, gray-masked out lips
   8. Painted white over iris areas of eyes with soft brush; Color Dodge, Fill 50%
   9. Hue/Saturation adjustment layer [colorize checked] 50 50 0, Linear Burn, Fill 15%, masked out darkest line areas
  10. With all layers off, other than the original photo, select > color range > midtones, fill with 50% gray, g-blur 3; set to Color Burn, Fill 25% (afterwards, remember to turn all the other layers back on)
  11. Painted thick, soft lines over wrinkles with black; Color Burn, Fill 5%
  12. Painted thin, soft lines over wrinkles with black; Color Burn, Fill 10%
  13. Painted soft white over areas of face catching the most light (except the nose, which got blown out with any added highlights), Color Dodge, Fill 10%
  14. Curves adjustment layer, slight "S" curve, set to Luminosity, Fill 50%

manoa@manoa:~$ cd separate+-0.5.3/
manoa@manoa:~/separate+-0.5.3$ make
gcc -g `pkg-config gimp-2.0 --cflags` `pkg-config gimpui-2.0 --cflags` `pkg-config gtk+-2.0 --cflags` `pkg-config lcms --cflags` -O3 -Wall -DENABLE_COLOR_MANAGEMENT -DENABLE_NLS -DGETTEXT_PACKAGE="\"gimp20-separate\"" -DSEPARATE_SEPARATE -DUSE_ICC_BUTTON -c separate.c
Package gimp-2.0 was not found in the pkg-config search path.
Perhaps you should add the directory containing `gimp-2.0.pc'
to the PKG_CONFIG_PATH environment variable
No package 'gimp-2.0' found
Package gimpui-2.0 was not found in the pkg-config search path.
Perhaps you should add the directory containing `gimpui-2.0.pc'
to the PKG_CONFIG_PATH environment variable
No package 'gimpui-2.0' found
Package gtk+-2.0 was not found in the pkg-config search path.
Perhaps you should add the directory containing `gtk+-2.0.pc'
to the PKG_CONFIG_PATH environment variable
No package 'gtk+-2.0' found
Package lcms was not found in the pkg-config search path.
Perhaps you should add the directory containing `lcms.pc'
to the PKG_CONFIG_PATH environment variable
No package 'lcms' found
separate.c:22:20: error: stdlib.h: No such file or directory
separate.c:23:19: error: stdio.h: No such file or directory
separate.c:24:20: error: string.h: No such file or directory
separate.c:26:21: error: gtk/gtk.h: No such file or directory
separate.c:28:26: error: libgimp/gimp.h: No such file or directory
separate.c:29:28: error: libgimp/gimpui.h: No such file or directory
In file included from libgimp/stdplugins-intl.h:6,
                 from separate.c:31:
libgimp/gettext.h:6:24: error: glib/gi18n.h: No such file or directory
In file included from separate.c:33:
separate.h:4:18: error: lcms.h: No such file or directory
In file included from separate.c:33:
separate.h:9: błąd: expected `=,, `,,, `;,, `asm, or `__attribute__, before `SeparateRenderingIntent,
separate.h:22: błąd: expected specifier-qualifier-list before `gboolean,
separate.h:34: błąd: expected specifier-qualifier-list before `SeparateRenderingIntent,
separate.h:40: błąd: expected specifier-qualifier-list before `gint8,
separate.h:46: błąd: expected specifier-qualifier-list before `gchar,
In file included from separate.c:34:
icon.h:7: błąd: expected `=,, `,,, `;,, `asm, or `__attribute__, before `separate_icon_cmyk,
icon.h:140: błąd: expected `=,, `,,, `;,, `asm, or `__attribute__, before `separate_icon_duotone,
In file included from separate.c:36:
platform.h:25:1: warning: "USE_ICC_BUTTON" redefined
<command-line>: warning: this is the location of the previous definition
In file included from separate.c:37:
util.h:6: błąd: expected `=,, `,,, `;,, `asm, or `__attribute__, before `separate_is_CMYK,
util.h:11: błąd: expected `=,, `,,, `;,, `asm, or `__attribute__, before `separate_create_RGB,
util.h:13: błąd: expected `=,, `,,, `;,, `asm, or `__attribute__, before `separate_create_planes_grey,
util.h:15: błąd: expected `=,, `,,, `;,, `asm, or `__attribute__, before `separate_create_planes_CMYK,
util.h:17: błąd: expected `=,, `,,, `;,, `asm, or `__attribute__, before `separate_create_planes_Duotone,
util.h:20: błąd: expected declaration specifiers or `..., before `gboolean,
util.h:23: błąd: expected `=,, `,,, `;,, `asm, or `__attribute__, before `*, token
In file included from separate.c:38:
tiff.h:4: błąd: expected `), before `*, token
In file included from separate.c:40:
iccbutton.h:9:27: error: gtk/gtkbutton.h: No such file or directory
iccbutton.h:10:18: error: lcms.h: No such file or directory
In file included from separate.c:40:
iccbutton.h:34: błąd: expected `=,, `,,, `;,, `asm, or `__attribute__, before `enum,
iccbutton.h:54: błąd: expected specifier-qualifier-list before `GtkButton,
iccbutton.h:79: błąd: expected specifier-qualifier-list before `GtkButtonClass,
iccbutton.h:84: błąd: expected `=,, `,,, `;,, `asm, or `__attribute__, before `icc_button_get_type,
iccbutton.h:85: błąd: expected `=,, `,,, `;,, `asm, or `__attribute__, before `*, token

iccbutton.h:88: ogłupiony przez wcześniejsze błędy, poddaje się
make: *** [separate.o] Błąd 1
manoa@manoa:~/separate+-0.5.3$ sudo make install
[sudo] password for manoa: 
gcc -g `pkg-config gimp-2.0 --cflags` `pkg-config gimpui-2.0 --cflags` `pkg-config gtk+-2.0 --cflags` `pkg-config lcms --cflags` -O3 -Wall -DENABLE_COLOR_MANAGEMENT -DENABLE_NLS -DGETTEXT_PACKAGE="\"gimp20-separate\"" -DSEPARATE_SEPARATE -DUSE_ICC_BUTTON -c separate.c
Package gimp-2.0 was not found in the pkg-config search path.
Perhaps you should add the directory containing `gimp-2.0.pc'
to the PKG_CONFIG_PATH environment variable
No package 'gimp-2.0' found
Package gimpui-2.0 was not found in the pkg-config search path.
Perhaps you should add the directory containing `gimpui-2.0.pc'
to the PKG_CONFIG_PATH environment variable
No package 'gimpui-2.0' found
Package gtk+-2.0 was not found in the pkg-config search path.
Perhaps you should add the directory containing `gtk+-2.0.pc'
to the PKG_CONFIG_PATH environment variable
No package 'gtk+-2.0' found
Package lcms was not found in the pkg-config search path.
Perhaps you should add the directory containing `lcms.pc'
to the PKG_CONFIG_PATH environment variable
No package 'lcms' found
separate.c:22:20: error: stdlib.h: No such file or directory
separate.c:23:19: error: stdio.h: No such file or directory
separate.c:24:20: error: string.h: No such file or directory
separate.c:26:21: error: gtk/gtk.h: No such file or directory
separate.c:28:26: error: libgimp/gimp.h: No such file or directory
separate.c:29:28: error: libgimp/gimpui.h: No such file or directory
In file included from libgimp/stdplugins-intl.h:6,
                 from separate.c:31:
libgimp/gettext.h:6:24: error: glib/gi18n.h: No such file or directory
In file included from separate.c:33:
separate.h:4:18: error: lcms.h: No such file or directory
In file included from separate.c:33:
separate.h:9: błąd: expected `=,, `,,, `;,, `asm, or `__attribute__, before `SeparateRenderingIntent,
separate.h:22: błąd: expected specifier-qualifier-list before `gboolean,
separate.h:34: błąd: expected specifier-qualifier-list before `SeparateRenderingIntent,
separate.h:40: błąd: expected specifier-qualifier-list before `gint8,
separate.h:46: błąd: expected specifier-qualifier-list before `gchar,
In file included from separate.c:34:
icon.h:7: błąd: expected `=,, `,,, `;,, `asm, or `__attribute__, before `separate_icon_cmyk,
icon.h:140: błąd: expected `=,, `,,, `;,, `asm, or `__attribute__, before `separate_icon_duotone,
In file included from separate.c:36:
platform.h:25:1: warning: "USE_ICC_BUTTON" redefined
<command-line>: warning: this is the location of the previous definition
In file included from separate.c:37:
util.h:6: błąd: expected `=,, `,,, `;,, `asm, or `__attribute__, before `separate_is_CMYK,
util.h:11: błąd: expected `=,, `,,, `;,, `asm, or `__attribute__, before `separate_create_RGB,
util.h:13: błąd: expected `=,, `,,, `;,, `asm, or `__attribute__, before `separate_create_planes_grey,
util.h:15: błąd: expected `=,, `,,, `;,, `asm, or `__attribute__, before `separate_create_planes_CMYK,
util.h:17: błąd: expected `=,, `,,, `;,, `asm, or `__attribute__, before `separate_create_planes_Duotone,
util.h:20: błąd: expected declaration specifiers or `..., before `gboolean,
util.h:23: błąd: expected `=,, `,,, `;,, `asm, or `__attribute__, before `*, token
In file included from separate.c:38:
tiff.h:4: błąd: expected `), before `*, token
In file included from separate.c:40:
iccbutton.h:9:27: error: gtk/gtkbutton.h: No such file or directory
iccbutton.h:10:18: error: lcms.h: No such file or directory
In file included from separate.c:40:
iccbutton.h:34: błąd: expected `=,, `,,, `;,, `asm, or `__attribute__, before `enum,
iccbutton.h:54: błąd: expected specifier-qualifier-list before `GtkButton,
iccbutton.h:79: błąd: expected specifier-qualifier-list before `GtkButtonClass,
iccbutton.h:84: błąd: expected `=,, `,,, `;,, `asm, or `__attribute__, before `icc_button_get_type,
iccbutton.h:85: błąd: expected `=,, `,,, `;,, `asm, or `__attribute__, before `*, token

iccbutton.h:88: ogłupiony przez wcześniejsze błędy, poddaje się
make: *** [separate.o] Błąd 1
manoa@manoa:~/separate+-0.5.3$