The anatomy of modern gold threads

One of the hardest things in recreating medieval goldwork embroidery is finding embroidery materials that are similar to those used in the past. Although the composition of the gold threads used is not routinely stated in publications and museum catalogues, generally speaking, modern threads contain less real gold or even none at all. But what else can be learned from having a closer look at them? Out come the digital microscope and some matches.

Although I have quite a collection of gold threads, I am going to take apart a few key ones that you are probably familiar with too:
- imitation Japanese thread (#8 from Golden Threads)
- passing thread (Stech 120/130 from M. Maurer)
- "real" gold passing thread (Stech 120/130 Echt Gold with silken core from M. Maurer)
- pure goldthread (vintage Japanese from Hauser Gallery)
All these threads have a thin foil that's wrapped around a textile core thread.

Let's start by having a look at how the foil has been wrapped around the core thread. Interestingly, you can see the core thread between the foil wraps in all specimens. The glare of the gold is such that we don't see this with the naked eye. If you click through the above picture gallery, you will see that the two Japanese threads are Z-spun and the two passing threads are S-spun. You'll also see that the width of the foil is much greater for the Japanese threads than for the passing threads. This probably explains why you don't have pesky pieces of foil standing up in tight turns when you are using passing thread. The changes of you "folding" a single wrap in a turn is less. It is more likely that you'll push two wraps a little apart with your couching thread.

To quantify things a bit: there are c. 13 wraps/cm for the imitation Jap, c. 16.5/cm for the pure gold thread and c. 64 wraps/cm for both passing threads.

Let's unwrap the foil from the core and see what it's actually made of. This exercise reveals the biggest difference between the Japanese threads and the Stech. You can clearly see in the pictures above that both Japanese threads have a golden foil on the outside of the strips and a substrate on the inside. It is white in the imitation Jap and brownish in the real gold thread. The latter is very likely a special high-quality paper, but the white stuff might be an artificial membrane.

The foil of the Stech looks very differently and behaves very differently: it really is a strip of metal without another material. It stretches considerably upon unwrapping. In the pictures, you can see that the foil has a silver colour on one side and a golden colour on the other. According to the manufacturer, the normal Stech consists of a silvered copper thread which is then very thinly gilded on one side. The Stech Echt Gold is a pure silver thread that is then gilded with pure gold on one side resulting in a higher karate.

Above, you see pictures of the cores of the different gold theads. All are yellow, except for the vintage pure gold thread which has a more reddish hue. To determine if they are made of real silk or polyester, I have burnt them by holding them in a flame with tweezers. The core of the imitation Japanese thread burnt with a small flame and the smell was one of something being burnt. The core of the Stech burnt with angry sparks and there was no smell at all. The core of the Stech Echt Gold burnt very quickly with a faint smell of something being burnt. The core of the Pure Gold thread burnt very quickly, but I could not detect a smell. The results hint at the core of the imitation Jap being cotton, the core of the Stech being artificial and the cores of the Stech Echt Gold and the Pure Gold thread being silk.

How do these results compare to the gold threads that were being used in medieval embroidery? Find out in next week's blog post!