Sheer Dress

Portrait of a Lady, by Samuel Sidley
Fabric
Sheer or semi-sheer fabrics of the 1860s came in cottons, silks and wools (linen wasn't typically used for dresses). In some cases, it is hard to tell if an original garment is cotton or wool because the feel of both types of those sheers is almost the same.

Sheer dresses could be made from either solid-colored or patterned fabric, just as regular dresses were. Solids were fairly rare and almost always silk since dyes weren't dependably colorfast in cottons and wools. Solid white sheers could be worn in any of the three fibers. But even solid colors usually had some sort of design in the fabric weave itself.

Design
While many sheer dresses are designed much like regular dresses - round collar, bishop sleeves, and so on - sheer dresses could also be designed for maximum coolness. It's quite common to see sheer dresses with v-necklines and open sleeve designs.

On a sheer, undersleeves are not generally required (though some ladies still wore them). And it's also "allowed" to have a v-neck or crossover bodice that has no closure, such as buttons or hooks. The bodice is simply held shut with a small pin.

Tucks on the bodice, sleeves
and skirt create interest
Trim
Trimming on a sheer dress was treated rather differently than trim on a regular dress. Because the fabric was so delicate, and because the point of a sheer was to have a light-weight, airy dress, sheer dresses did not have heavy trim.

In fact, most sheers and semi-sheers were "self-trimmed" - that is, they were trimmed with pieces of their own fabric made into ruffles or ruching.

Large ruffles on the skirt create a "swishy" floating look. Tiny ruffles on the bodice, sleeves or skirt could be gathered and sewn on in lovely designs. Small ruffles were often cut on the bias (diagonally on the grain of the fabric) so they didn't even need to be hemmed. In addition to a gathered ruffle, strips of fabric trim could be pleated or ruched into lovely designs.

Tucks on a skirt or sleeves were not only ornamental, they also helped give body to the fabric. Since a tuck doubles the fabric on itself, it creates a dashing, darker stripe effect on the sheer fabric.

Gathers were often used - at the waist, on the sleeves, and even on the bodice. A beautiful effect is gathers on lengths of piping. This keeps the gathers even down the bodice and creates a wonderful geometric design.

An exception to the "no non-fabric trim" guideline is light-weight ribbon or soutache, or a fine, bias-cut strip of fabric. This was occasionally used either to highlight the self-fabric trim or to bind the edges of ruffles and ruching.
The fabric of the bodice is 
gathered onto small piping or cording

Construction
Sheer dresses are not only designed and trimmed differently from regular dresses, they are constructed differently.

Obviously, the goal of a sheer was coolness and airiness. Thus, wherever possible, lining is dispensed with. Lining on any 1860s dress was partly for the purpose of protecting the fashion fabric from body oils. Thus, you will find lining on sheers was generally only where the danger from body oils was greatest - on the lower part of the bodice and under the arms. Sometimes there is no lining at all and the lady relied on her undergarments to protect the dress.

This lady's lining fabric is clearly 

visible and her shoulders are left

bare under the fashion fabric
Lining fabric on a regular dress is attached to the fashion fabric at the armholes, shoulders, side-seams and waistband, and probably in some darts. But in sheers, the "connections" are often only at the waistband and side-seams. The lining neckline could be dropped as low as the chemise neckline. In fact, bodice lining is often almost a stand-alone garment in sheers. In some cases, it even fastens separately from the fashion fabric.

In many original photographs and paintings of ladies in sheer dresses, you can see the lining edge through the dress fabric. The lady's shoulders are often left bare except for the fashion fabric itself.

Accessories
Once again, the goal of a sheer was usually to have an airy, cool outfit. So you won't see tons of jewelry, watches, chatelaines, and such worn with sheer dresses. Heavy accessories could tear or snag the delicate fabric, not to mention look incongruous with the overall "floating" appearance. Earrings, a small brooch and possibly bracelets seem to be the extent of most ladies' jewelry with sheer ensembles.

However, it is common to see a lovely belt and/or a floral corsage with a sheer dress. Belts could be self fabric (stiffened with some heavier fabric underneath), or they could be a contrast color. Belts ranged from a simple solid colored ribbon to elaborate bows or buckles and rosettes.