For the knappers

[Auzoutdoor]

Hi guys I have heard that some people heat some rocks before knapping but cant seem to find any info on the subject.It must be to make it easier to work but do you then heat it again to get it hard again?Also can you do it to the stone you get from toilet tanks to make it a bit easier to knap.Thanks in advance
Cheers KIM

[Linc]

Some but not all knappable can be heat treated.It changes the hardness and chrystaline structure.Once heated it can't be heated again to return it original hardness.

I don't think there is anything you can do to change "Johnstone".You work it as is.

[Auzoutdoor]

Thnaks Linc does that mean it will not hold an edge as it is softer after heating?It seams a bit of a deep dark secret asa in all the articles to be found on the net I cant find any mention of it.
Thanks for any input here guys.
Cheers KIM

[DarkeGreen]

Use google as search on heat treating flint. There if more information on the net then you can read in a life time!

You can find even more by switching out words in your search.

[geno]

I was told to lay 4" of sand over your rocks and build a fire. just let the fire go out. when they cool you are good to go..

[Linc]

Kim,Heat treated material isn't soft,it is quite hard and will hold an edge.It is just softer than the original raw material.

Actually you only need an 1" or 2" of sand.It depends on the material you are heat treating.Some only need 350deg,some need a lot more.

[knife river]

The answer depends on what you mean by "hardness."  On the Mohs scale, nothing changes, but heat-treated stone becomes more brittle and breaks more easily.  That can be good if it's a very tough stone which is virtually unknappable when raw.  However, some knappers heat stone to temps just short of blowing it up to bring out the greatest color.  The knapping qualities suffer, though, and because the edge is super brittle, it will dull extremely quickly.

The trick is to heat the stone enough to enhance the knapping qualities but not so much that it loses it's other desirable traits.

We could probably come up with more complete answers if you told us what kind of stone you were thinking about heat treating.  Good luck!

[geno]

what is "johnstone" ??.

[ber643]

LOL - "John...", as in "Terlet" (as Archie Bunker used to say). Knappers mostly use the Tank Tops (I understand old ones are better).

[Auzoutdoor]

Thanks guys for the info I guess its just a trial and error thing and see what I come up with.I was thinking mostly about the Tank Top as it is cheap and easy to get for learning on.We dont have great supplies of knapping here in Auz that you guys have over there.Thanks again for all the help and keep the tips coming please.
Cheers KIM

[Molson]

Yes, treat Johnstone as you would Thunder Chert or Squartz!

[ncboman]

If you learn to work obsidian first, knapping other materials is more easily understood.

[Auzoutdoor]

Ok for a bit of practice today I tried the old bottle to b/head thing and came up with this so far.The flakes are getting bigger and going further across so things are improving.Heaps easier than the china.
Cheers KIM

[Linc]

Looking good Kim. It would be a good idea to sharpen your pressure flaker. It will require a lot less force to remove flakes.