This is a lovely item, with striking decoration and several interesting design features. Unfortunately, I have not been able to locate high-resolution images of the piece, or any details other than the limited write up on the museum site; so what is below is my best take on the piece.

Description: "Reliquary bag (bursa), Rhineland, 14th and 15th cent., Linen with silk embroidery, metal-wrapped thread"

Origin: Germany
Period: 14th-15th century
Current location: Museum Schnutgen, Koln, Germany
Museum number: P 870

Current Museum page:
http://www.museum-schnuetgen.de/default.aspx?s=1412&kat=22
See also:
http://www.kulturelles-erbe-koeln.de/documents/obj/05110003


Personal Observations:
The first thing that jumps out is that this piece uses a variation of cushion stitch extensively, as well as the usual brick stitch. There is another example of cushion stitch to be seen in pattern Y-008A.

A close examination of the best photo available reveals several interesting details of construction: Most noticeably, instead of closing with a drawstring like many other examples, this bag closes with a flap and a button. It cannot be determined from the photo if the back of the bag is embroidered, but the fold over flap, and the fact that the flap is embroidered with the same pattern, upside down, suggest that this is so. The flap's bottom corners are rounded, and on the left, a bit of the bags lining is visible. The flap is secured by a what appears to be a cloth button at the center bottom of the flap. In addition, there are the remains of wax seals at the center, and left and right ends. The center seal still secures a spiral fingerloop braid of tan and green silk.

There are four tassels attached to the bag, two at the bottom corners, two 1/4 of the way down the sides of the bag. These tassels are bound in turks-head knots.

It cannot be determined from the photo whether the bag was made in two pieces stitched together, or one piece folded at the bottom. The upside-down pattern on the flap suggests the former, but is speculation. In any case, The edges of the bag (bottom, sides, and around the edge of the flap) are decorated with a double edge finishing: One a tan and green double pattern as seen in other examples (See Y-011), and a line of brown.     

Fabric count: ~50 threads per inch (computed from photograph and given dimensions)

Colors noted:
Light golden brown
Dark green
Black
Off white
Metallic gold    

References:
None
 
Images:
http://www.kulturelles-erbe-koeln.de/documents/obj/05110003/rba_d029062

Patterns:
http://wymarc.com/images/patterns/pdf/Y013A.pdf
http://wymarc.com/images/patterns/pdf/Y013B.pdf
http://wymarc.com/images/patterns/pdf/Y013C.pdf
http://wymarc.com/images/patterns/pdf/Y013D.pdf