As you may have gathered from this blog or other texts of the 18th century, sex was a common amusement of the 18th century. The new freedoms of speech and ideas of the Enlightenment allowed for sex to not be talked of only behind closed doors but also commonly read about and seen in the art of the time. Yes, sex was everywhere and everyone was having it. That is why there were so many illegitimate children being born of aristocratic ladies and then quickly shipped off to be raised by foster mothers, preferably in France. But for as long as humans have been having sex for recreation, there has been means of contraception. The 18th century was no exception to this. Although, it may not seem so if you've been keeping up with your weekly tarts.
The most common and ineffective use of contraception in the 18th century is one still commonly practiced today, "pulling out." Coitus Interruptus was popular based on the fact that it was cheap and handy. That is, until its participants realized how ineffective it really was.
For those more willing to spend some money and more worried about getting a venereal disease there were condoms (image at right circa 1900). These were commonly called, "machines" and made from the intestines of various animals, usually sheep. They were produced in Covent Garden (or course) and distributed at the various sleazy shops in the same area. When you bought one of these "machines" you bought it with the intention of using it more than once. The condom usually came in packaging for safekeeping and the very end was folded over and stitched with a silk ribbon (usually pink) at the end to tie and secure. Washing was recommended but was probably not commonly done. Although these sheaths may have helped protect against STDs they weren't that successful as contraceptives; they were semi-permeable. Water could go right through them. Not to mention they were prone to tears. So that's where all those illegitimate kids came from.