Ironically this girl's beautiful golden hair is made with rust!
Raw Umber - The poor artist's best friend
The reason certain methods and materials were used was often a financial
one. In the middle ages( 11th - 16th centuries) rare green pigments cost
more, so were used less.
Raw Umber was the cheapest colour to manufacture. It was made from iron-rich mud found in the Dutch countryside, or rust scraped from old iron pots or plates. The rust was ground to dust between two millstones. There are 1 or 2 windmills in Holland today that still grind oil paint pigment. A little nut or linseed oil added to the rust became the base for most Northern European Oil Painting ( first used by van Eyck & the mysterious Artist of Flemalle ).
An added advantage for us is that rust shows up well on x-rays, so we
can see the underpainting of those great masterpieces.
Paneljacking
Panel manufacture was costly and time consuming. Paper had yet to be imported from the East and when it was it cost a church's fortune. Often a painter would nip out to the local dealer and buy a rubbish artwork - just to scrape it down and use the panel it was on. We can still see remnants of these unfortunate paintings using x-ray.
Linseed Oil
Oil derived from the flax plant (The same plant used to make linen). It grows plentifully in North Africa and Europe. Medieval linseed oil was thinner than the processed oil we buy today, and it dried very slowly. 3 Months could go by before flies would stop sticking to a painting.
Johannes van Eyck came up with a cunning way to improve oil and make it suitable for painting. The complicated process involves putting it in an open bottle and leaving it in the sun. For about 3 months. And occasionally scooping off the mucilage (impurities like dust, bacteria). Linseed oil becomes quite gloopy when reduced in this way, and dries in a few days. You can improve your own linseed oil by leaving it open with a cloth or something over it to stop the bugs getting in.
Sable Brushes - And a Hair of the Dog That Bit You
The best brushes for oil painting are not those horrific scratchy things they sell in art shops, but soft, fine sable-hair brushes. Combine these soft, thin brushes with smooth wooden panels and you have an incredibly fine way of painting. Medieval artists could achieve their impressive detail this way. Modern artificial watercolour brushes work, but eventually melt in turpentine.
Many types of hair work well in brush manufacture. If you want a high quality brush cut some of your own hair and clamp it in a cheap brush-handle. So easy, so cheap, so ... weird.
Monks and Bishops
We know many masters bought materials from monasteries. Their receipts show large quantities for oils, woods, waxes, honey and wines... all for Painting, of course ;o) ! Moreover, materials for Holy works had to be blessed ( like Halaal meat ) so it became convenient to acquire materials and have them sanctified in one go.
Before the invention of chemical paint treatment, paintings would accumulate mucilage(dust, bacteria, insects, etc), which dulled the image. Cunning artists convinced the churches to use the finest wine. Of course when any liquid is wiped onto a dulled painting the mucilage easily wipes off and the painting is gloriously bright again... but the bishops who funded the restorations didn't know that soapy water works just as well.
Models
One of the greatest inventions of Oil Painting is the posing model. During the Dark Ages it was considered unholy to create an image of anyone but religious figures, and since no one knew what they looked like they were just made up. Brave artists from Flanders and Italy defied this doctrine when they used models as reference for paintings. There was a huge leap of realism in Oil Painting when models and other reference were used. Some models worked professionally - try and spot Pater Genys in a few Dutch paintings.
A wee bit of Fixative
Medieval masters used urine to prevent drawings from smudging. Urine used to be a very useful and lucrative substance (loo-creative?). In medieval times urine dealers would come and take, well, the piss from your home. It was unwanted, and given freely, but its uses were wide and the urine dealers made quite a packet. This profession has always caused a chuckle, hence the term, "Taking the piss".
Paper
Paper was seldom seen in Medieval times, it was frightfully expensive and difficult to come by. Vellum (goatskin) was cheaper and easier to produce ( not necessarily for the goat ). Most artists used Silverpoint instead. A bit of secret paper trade did occur between China and Europe, and a few drawings have survived. Once the secret of papermaking spread to the Occident it changed the way people painted.
Silverpoint
Highly skilled artists produced drawings using a silver pin and a board painted with chalk or lime powder. The silver instantly reacts with the chalk leaving an incredibly delicate line. Some of the most beautiful drawings ever created were done using silverpoint, incredibly so because it is not possible to 'rub out' a line. Most art studios required aspiring artists to produce a silverpoint drawing before being accepted. It is the mark of true precision.
Want to try Silverpoint for yourself?
Buy a Silverpoint pen from me. Silverpoint drawing is easy to do, though challenging to master.
You can use an acrylic-primer painted board with acceptable results. Some fabric paints are chalk(calcium) based and work very well with silverpoint pens.
Miniatures - A Crusade to revise a little
Alas! Medievil [sic] Churches were not keen on paintings of just ordinary people, why, that elevated their status to that of any religious figure! In their attempt to rewrite history in their favour the militant arm of the Church confiscated or destroyed any secular artworks they saw. Thus miniature paintings became a way of remembering loved ones and history, because they could be carried about one's person or hidden under the dog or some such.
Master miniature painters like Hubert and Johannes van Eyck, having years of experience illustrating religious documents, were able to produce tiny paintings with enormous detail. They carried their eye for detail through to their larger works, once the furor had died down.