The Great Plate Debate

[dubsartur]

This is a placeholder because an independent scholar and art restorer named Chris Dobson has brought up the problem whether much European plate armour was blued or blackened before the sixteenth century (that is, it was heated evenly until it was coloured, and then either organic material was burned on to it, or it was rapidly cooled by quenching to lock coloured oxides to the surface).  Almost all armour before that period has either been allowed to badly rust, or scrubbed back to bare steel, or both at some time after its working life.  Therefore, its almost impossible to determine the original surface finish by examining surviving armour from the fifteenth century or earlier.

Shiny surfaces are extremely hard to photograph or paint, and before about 1430 artists didn't really try to depict the outward surface of things as the eye would see them.  Many people say that by sometime in the fifteenth century, there are so many very detailed and lifelike pieces of art with dark armour that it was probably a common thing.  Earlier its hard to decide how to interpret the art because "this is an expensive painting, use lots of gold, silver, and precious colours" was a thing that patrons asked.  There is lots of medieval art where the artist clearly mixed up a small palette of colours and stuck with that so the work would go quicker. So when we see something like this:



its hard to make a convincing argument for why the first knight's surcote, the second knight's helm, the young man's tunic, and the old man's hair are all the same grey colour.  You can be more confident with someone like Hieronymus Bosch in the sixteenth century who really seems to want the head of the crossbow bolt and the mittens of plate to look different.



Since the argument is in an expensive book which arrives slowly by courier and has arguments which use a wide variety of evidence in ways that are sometimes convincing and sometimes not, the quality of the online discussion has not been the best (lots of comments by people who have not read the thing or have only read parts).  For example, Chris Dobson is very optimistic about seeing things as authentic which most people agree were made in the 19th or 20th century (occasionally by cutting up medieval armour).  I have to be careful how much time I put in so I don't get distracted from things that would pay in money or CV lines or get me out the door.

This thread is pretty good on polishing.

[Jubal]

Does the blued/blackened heating process have a practical advantage, or is it largely an aesthetic choice?

[dubsartur]

Blackening and bluing give some resistance to rust (more with the processes where you burn on some organic substance, Theophilius says that spurs for clerks can be blackened by burning horn onto the iron).  Some ancient, medieval, and sixteenth-century armour was tinned which is shiny and rust-resistant. Treatments in these families (or modern ones with a painted-on solution which creates an oxide layer) used to be common for firearms back when they had more steel and less polymer in them.

In the bit that I have read, Chris Dobson does not talk about how the colour black and plays between light and shadow were extremely fashionable in the late sixteenth, early seventeenth century which is when we have so much surviving blackened armour.  In the later middle ages, bright colours like red and glistening cloth-of-gold (with patterns made from thread wrapped in gold) were more in fashion.

Edit: A good example of the problems of interpreting colours in medieval art is the Grandes Chroniques de France in the British Library.



The background is filled in with colours and patterns because horror vacui.  The crown and the knees and elbows of some of the armours are gold leaf.  Does that mean that they are all gold/gilt, or that some represent brass and bronze?  There was plenty of copper-alloy armour in the later middle ages, it was not the strongest material but it was competitive with most irons and steels, it looked shiny and it did not corrode as easily as iron and steel.  And gold leaf is the easiest way to make a shiny yellow surface with medieval technology, and the illuminators had already been given a certain number of florins' worth of gold to decorate this manuscript.

[dubsartur]

Here is an extant helmet from the sixteenth century which still has a dull grey oxide finish wherever it is not etched and gilt.



One problem is that capturing the surface of reflective surfaces is hard.  Here are some knives by Tod Cutler under one set of lighting



Here is one of the same batch of knives, made from the same steel using the same tools and the same model, under different light.



One looks more white, the other looks more blue.

I'm just looking for something to post about which is more pleasant than the state of the news media or the follies of local politicians.

[Jubal]

I am in favour of more medieval arms & armour posts, I love reading this sort of thing

And yes, light can make an enormous difference photographically. I also don't think I'd encountered the idea of horror vacui before this thread, that's a useful concept to mull over. Some medieval art does use a lot of empty space, especially if it's marginal or illustrative, but it's interesting where artists do go for that sort of heavy patterning.

You might also be interested in the thread I just posted on disabling strikes in game rules, which you have more the weapon knowledge for than myself.

[dubsartur]

Craig Johnson and Nathan Craig at the Oakeshott Institute have a blog post and a vlog (YouTube - Invidious) about the finish of European sword blades since the year 1000.

If you look at say a cheap pair of safety scissors today, you will probably see a 'satin' finish from medium-fine grit leaving fine parallel lines.  They see traces of a different approach on medieval swords, with a grind with a rough grit one way to remove hammer marks and forge scale, and a much finer grind crossways which gave a shinier surface with a few very visible scratches from the coarse grit. 

[dubsartur]

GreenLeaf Workshop in the UK has a video on oil blackening steel https://www.youtube.com/watch?v=1APNUh5GTKA  It is good to know that from the Iliad into the 16th century, Europeans talk about quenching ferrous metals in water.  Today metalworkers often use various oils because they don't cool the metal as quickly so the metal is less likely to crack, but I don't know a source for that up to the 16th century.  Around 1130 Theophilius describes techniques such as burning a cow's horn onto spurs to blacken them if the customer can't afford gilding or does not want to spend, but dipping hot metal in oil was not something ironworkers did on every project.

[Jubal]

If one wants to cool the metal more slowly - and this may be a daft question - does one need oil, as opposed to just e.g. heated water that's therefore closer to the metal temp and will result in a less sharp heat transfer? Or is the metal so hot for working that e.g. cooling it in 70C water really doesn't make much difference?

[dubsartur]

I don't have any hot metalworking experience and Physics 12 was too long ago but I think boiling points have something to do with why water cools hot iron quicker than plant oils or rock oil.  Water boils at 100°C, linseed oil (just to pick one plant oil) at 340°C.  https://pubchem.ncbi.nlm.nih.gov/compound/Linseed-Oil

[Pentagathus]

Yes this sounds very likely - evaporation is why water be make people cold so I would guess it also makes metal cold.

[dubsartur]

People often demonstrate quenching a blade in oil, pulling it out, watching it catch on fire, quenching it in oil again, and repeating until it stops igniting.  https://yewtu.be/iQ4_mWnGn6E?t=411

Quenching plate armour is difficult because its large thin pieces with complex three-dimensional shapes which can easily distort.  Armourers today usually fasten the parts temporarily together with wire.  I remember that the PBS Nova on reproducing a Greenwich armour had some good clips https://www.pbs.org/video/secrets-shining-knight-preview-em5biq/

Europeans wrote basically nothing about iron production and ironworking before the 16th century.  It was just another dirty manual trade like pottery or pig farming.  Theophilius only touches on ironworking because he decided he wanted to write about how to make tools for working glass, ivory, and precious metals.  And iron is unstable and often has villainous things done to it by conservators collectors and metal detectorists, whether that is assigning conscripts to scrub the palace armoury clean, or baking the sword they just dug up to stabilize it, or applying modern browning and bluing solutions.  So its hard to be sure of lots of the details, especially because arms & armour studies never became institutionalized.  Its a few curators, a few archaeologists, and a lot of people without academic jobs.

[Jubal]

Yes, a 340 boiling points sounds like it'd make rather a lot of difference! That makes sense, thanks both.

[dubsartur]

The difference in boiling points is why things are fried in hot oil (and why deep friers are so dangerous).