Patina Question

[-=METACOM=-]

Now I know this question is broad, I will try to narrow it down a bit. I am wondering how long it generally takes for a patina to form. Let's take New England argillite for example. Could I expect a patina to form on freshly knapped stone within, say 100, 200, or 300 years, or is this something that takes well over a thousand.

I am aware that different materials under different conditions would yield different results, so lets just stick with argillite. I'm just looking for a very approximate answer, hoping someone has an idea.

TIA

[sneakygroundbuzzard]

i know some modern knappers who bury there points for a year or so and when they dig them up they already have a patina

i would say the longer the material is exposed to the elements,the more patina it will have and deeper into the stone it will be

[BabaORiley]

Yeah that is an interesting thought there Meta. Maybe the type of soil, the acidity and other elements of the soil, the climate i.e. like cold winters with hard freezes as opposed to more temperate climates. Hmm...great thought.

[Ron Kelley]

Even exposure to rain and sun will form a patina. You are right that happens on some lithics a lot faster than on others. Different climates make a huge difference in how fast the patina is formed.

[Pinetree1]

The answer is, there is no answer! Too many variables. That's why it's important to know as many variables as possible when making an assumption. I hope that helps you some.😀

[Scorpion68]

Hey ya'll - there was a post "What is Patina on an Artifact" in 2011 that Painshill indicated didn't crossover when the software was updated; however, they do define Patina as "Patina on chert is caused by carbonic acid from atmosphere that causes desilisification on the surface of chert, at the same time microbes invade microfractures and start eating the chert while metabolizing other nutrients and produce a metabolite which is silicified. These metabolitic by-products and microbes die leaving a micro-residue. Minerals, silica acid precipitate and fossilize the microbial residue to produce semi-crystalline biopolymers. These biopolymer structures are not completely crystalline and have a lot of defects in the lattice and void dislocations." Now some of the old timers may remember this post because Cliff came back with
"Come on, Jack, nobody can really read that, hahaha. The simple answer to the question "What is patina on an artifact?" is: Silicified dead microbes and microbe poop!(as Doc Gramly puts it)". Ok - besides the walk down memory lane, IMO the process that Jack (greywolf22) originally described would take considerable time like 100 - 1000's of years. I don't know if this thread ever made it over the software void but it's listed on the internet.

[Scorpion68]

Hey all - there was a 2011 thread regarding Patina but Painshill indicated that it didn't make the transfer over when the software was updated on AH.com. A very technical definition was given by greywolf22 (Jack) but was refined by Cliff who said " Patina is silicified dead microbes and microbe poop. The silicification process would probably take considerable time and as has already been said, too many variables enter into the question to define a timeline.

[Scorpion68]

My original post somehow disappeared and was fixed by Josh. So ya'll can see the initial description of Patina. Have a chuckle on me.....

[Ron Kelley]

Hey Chuckle It's the gremlins having their fun again

[-=METACOM=-]

I figured it wouldn't be very answerable. As always, thanks guys

[CMD]

Here is the thread that Chuck referenced:

https://forums.arrowheads.com/forum/general-discussion-gc5/artifact-questions-answers-gc9/202631-patination-of-lithics

In my experience, with the passage of time collecting, the accumulation of experience in other words, one can judge patina on a particular material well enough to distinguish an early point made of argiliite(or a different lithic) from a later point made of argillite. This helps with surface found artifacts out of context because it's just too easy to be stumped in trying to type a find in the first place. Depth or degree of patina can be the difference in deciding what type of point you found. It can be a very helpful clue. I have points that exhibit the deepest patina I've seen on argillite, and on Attleboro Red rhyolite, for instance. Judging the patina helped date those points, relatively speaking. But, you cannot really expect a visual guide of patina over time with argillite(or other lithic). I guess someone could make an effort in that direction, I'm just not aware if it exists.

[Kyflintguy]

Lots of variables like was said, environmental conditions can also factor in... Dry caves, Wet caves, anaerobic enviroments, open air enviroments, Mineral and chemical contents in the soil or water, light exposure and then you throw in materials with tendencies to react differently depending on environment. The possibilities are endless.

[-=METACOM=-]

Very helpful. And being able to say "this point is probably older than this point" is mainly what I'm interested for. Also, I'd like to be able to discern damage, scratches or markings on hard stone as before or after the use of plows.