All manner of threads appear in advertisements of the 18th and 19th century, including silk.  Looking at extant garments you will find various weights of silk typically used for silk and wool.  It was available in a variety of colors to suit any need.  

• Our Fine Silk Sewing Thread is suitable for your most delicate sewing needs, such as sewing on fine silk gauze, and comes on a 200 meter spool.  
• It can be used in a sewing machine if required.  
• Our Fine Silk Sewing Thread is available in white only.