At the beginning of gut strings, making them was pretty simple. There were few descriptions of string construction until the 16th century. Still, from the available data, especially the number of gut strands that went into making 'oud strings, according to Al Kindi, it is clear they have used what became known in later years as "whole gut" production, which is a process where the cleaned intestine is twisted as it comes from the animal.
The anatomy of the intestine is that of a curve, where one side of the tube is longer than the other. So, the shorter inside becomes tight with the whole tube stretched straight before, the longer outside curve. With whole gut production, it is impossible to align the fibers in the gut properly, and the strings made thusly tend to be weak and false.
Sometime in the 16th century, someone came up with a technology to solve this problem. I don't know where it happened, but I suspect the innovation occurred somewhere in the Saxony region, perhaps in Markneukirchen or Munich. The solution was to split the gut lengthwise to create two ribbons that could be stretched and aligned in a more rational structure, thereby making a stronger string.
The image presented is of our first gut splitter that I received from Glen Bjorkman of the Victor Surgical Gut Co. His family purchased the gut string-making business from the Armor Company in Chicago, IL, and this splitter was used in the Armor factory. It is a simple device that uses an old-fashioned double-sided razor blade to split the gut lengthwise. It is a hazardous device, and I can't say how many cuts we received from those blades. Even though we used warm water during the process, our hands would still get cold, and sometimes we would not realize a cut until we saw blood in the water. Still, it got us started with making strings, and it seemed like a reasonable risk at the time.