27. Period Science
I won the metalworking category for this one, due to the fine engraving on its surface.
What: A reproduction of a 16th century compass.
Materials: 0.0012” Brass, steel wire, solder, lampblack
Compasses were an essential, though frequently inaccurate, tool for navigation during the Renaissance. Initially, European compasses were basic iron needles or wires magnetized so as to point North, and then placed through a bit of straw or cork and set in a bowl of water. These were more of novelties than anything else, as they were essentially useless in a moving environment such as aboard a ship. Later compasses placed the needle on the underside of a card, which was then placed on a pivot in a wooden bowl. The entire card would rotate to indicate direction. These are called dry-card compasses, as they do not have the liquid medium added to smooth out extremes of motion seen in later compasses. The majority of surviving examples of dry-card compasses reveal brass cards, which is what I chose to go with.
I measured a circle on light sheet brass, which I cut using ordinary scissors after polishing with steel wool. I painted the face in white paint, over which I sketched in pencil and then engraved my pattern using an engraving tool. My compass face comes from the example in John Davis’ Seaman’s Secrets, published 1595. Rubbing alcohol was used to get the last of the paint off. This was then again polished with steel wool. I obtained soot from an oil lamp to highlight the card’s markings.
In period, wire was bent into a diamond shape and soldered to the back of the card. I did this, and magnetized the wires by stroking them with a bar magnet. The card fits onto a brass nail which has had its head removed. Additional drops of solder were used to help balance the card. I used a dapping punch to create the dimple in which the pivot pin rests, but had problems making sure the divot was deep enough without blowing out the top of the dent due to overstretching.
The compass does find north. However, it is unable to do so on its pivot point due to the friction between the card and the pivot. I have heard of crystal pivots being used to reduce friction (jade cups on quartz points), but this may be apocryphal. When placed on a float in a bowl of water, the card shows its charge and points north. Clearly, I need to go back and redesign both the pivot point and its point of contact.
1. Aczel, Amir D. The riddle of the compass. New York : Harcourt, 2001.
2. Davis, John. The seaman’s secrets. London: 1595. Available via the Early English Books Collection, Microfilm STC P&R 1750:4 or online at http://www.mcallen.lib.tx.us/books/seasecr/dseasec0.htm
3. Stevin, Simon. The haven-finding art. London: 1599 New York, Da Capo Press, 1968.