Some underwear is easy to date by the cut or the decoration, other items are almost timeless. 

This month I share with you a knitted silk undervest with a crocheted yoke that could date anywhere from 1880 to 1910. The eBay seller I purchased it from described it as a "vintage tank top", but ladies in the Victorian and Edwardian age would have recognized it as a vest or an undervest.

Very few of these vests seem to have survived the rigors of everyday wear and time, which is quite understandable given the tendency of fine knits to snag and run and the rough laundry practices of the time.

They were also probably not seen as a "special" item to be saved as a keepsake,  unlike a corset or special petticoat would be. (I think of my own lingerie drawers, remembering the silk nighties I've worn a few times and the innumerable nice knit underthings I've thrown out over the years due to snags or runs or stains!)

The design is very simple. The vest is a two by two rib knit, in what feels to be silk or a silk/cotton blend, with a crocheted yoke in a mercerized cotton thread. The knit section measures 21" (53cm) long, width is 13" (33cm) at the neck edge, and 6.25" (15.9cm) in the middle of the body, where the knit is not stretched.The side seams are sewn with a flat overlock stitch. The neck edge might be straight across or there might be a small amount of shaping at the armholes, but it is hard to tell because of the distortion of the yoke on the neck edge, and the effects of time on the sheer knitted gauze.  

The crochet yoke is 2.5" (6.4cm) deep in the center, 1.5" (3.9cm) deep under the arms. The shoulder straps are 1.5" (3.9cm) wide and 8.5" (21.6cm) long. The yoke is worked around the neck edge, not sewn to it, and the crochet thread is brought through the edge of the body as each row is worked. The yoke was not worked in the round, but it was worked as an edging and started horizontally, then using short rows the rows were shifted to the diagonal. The shoulder straps were worked separately, then the scalloped edging was added.

The yoke laid flat. The start of the edging is visible at the top left	The edging is worked through the edge of the body at every row
	Detail of the shoulder strap

(You can also see a museum accession number sewn into the back neck, but I have no idea which museum this was deaccessioned from)

Crochet Edgings and Trimmings

Modernly, most crochet is worked in the round, like a granny square, but in the Victorian era, the majority of crochet trimmings and edgings were worked "crosswise" or horizontally. The benefit of working an edging horizontally is that the length is not fixed from the start; the worker can make it as long or short as needed.

Here are two examples from Fancy work recreations: a complete guide to knitting, crochet, and home adornment (1885) by Eva Marie Niles (Archive.org). This book has a great many other edgings and trimmings in it aswell.

This rosette on page 190 is worked in the round...	...whereas this edging on page 161 is worked back and forth horizontally for several rows before the scallops and picot are added.

Instructions for crochet work... (1888) by Livetta White, Western lace manufacturing company, Chicago This book has a large number of crochet trimmings and edgings, from the very simple to the complex. There are also instructions for garments and fun things like tea cozies.
Rules and directions for the use of Finlayson, Bousfield & co.'s real Scotch linen crochet thread .. (1886) This simple pattern is from page 13

Additional Crochet Patterns

While these are outside the time frame for the DPP, they're just too pretty not to share!

Old and new designs in crochet corset covers and nightgown yokes ([19--]) by Sophi LaCroix

The Rundall book of edgings, medallions, insertions and tatting (1915)

The Priscilla crochet book, edgings and insertions, no. 2; a collection of beautiful and useful patterns, with directions for working (1916)