Rock Recipies from The
(This is slightly modified from a file posted to The
In the knapping community there are several ways to heat treat stone.
The following is a brief discription of three of these cooking methods:
abo techniques, use of a kiln, and use of a conventional roaster oven.
Following this brief outline is a listing of various materials, as well
as their cook and hold times. Enjoy!
The Abo way is in a pit, burying the spalls, bifaces and flakes under sand
or dirt, from several to about six inches deep. A campfire is built. The
next day the coals are scraped away from the surface and dried out
soil is removed. The spalls or bifaces are layered in and the soil
is replaced. Then the coals are placed back over and more fuel is added
so that the coals
remain for up to twelve hours. After a day or two the stone is dug
up and checked to see if it has been heat treated to satisfaction. Temperatures
range depending on stone thickness. A good place to start is that
a 1" biface buried 1" gets about to 600 - 650 degrees. For each 1/2" deeper
temperature drops 50 degrees. Thicker stone needs less heat, thinner stone
needs more to reach the same 600 - 650 degree results. Don't discount the
use of charcoal. It makes a great abo fire!
Kiln cooking rock is the most predictable method, especially if you have
a computerized control device as you have the most control. Ramp times
vary depending on material. A general rule of thumb is to dry your rock
out at 200° for 8 hours, then ramp-up in 50° increments (spalls
and smaller stone) until you reach the desired temperature, then hold for
the desired "soak" time. For larger stone reduce this ramp-up and down
times as larger stone does not absorb the heat as quickly as smaller sizes.
Additionally, there are several varieties of stone that should also be
ramped-up a bit slower: Harper, TX tabs, Rootbeer, Knife River, and Mozarkite(20-30°
per hour). Frisco, Pedernales amoebas and some of the darker rocks should
only be approached at 5° per hour. And it appears that ramp-down times
are just as crucial as ramp-up times. In most cases 30° per hour is
a good measure. Fuller kilns will ramp down slower than than emptier kilns.
Also, one should test their rock to see if it cooks better in whole or
slabs. Frisco, Montana agate, and Pedernales amoebas can only be cooked
as THIN spalls or as slabs up to about 5/16 inch, while Burlington, Flint
Ridge, Mozarkite, Knife River, and Kay County can easily be cooked whole.
Care should be taken to asure yourself that there are not any enhydros
(water pockets) in your rock as disasterous results can be obtained and
you may have to hunt far and wide for your kiln lid or garage door! Doug
Kries recommends ramping all rock up 5 degrees per hour and down 30 degrees
per hour, except for Burlington, Flint Ridge, and Kay County.
Roaster Oven Cooking
The roaster oven is a good middle ground when it comes to cooking. It is
less expensive than a computerized kiln (much!) yet gives more control
than a fire pit in your back yard. obviously less expensive than a kiln,
but also provides a bit of control. The negative is that some roasters
don't reach higher temps. The inner liner should be removed to allow higher
temperatures. Many use a sand or vermeculite "bath". This is done by place
spalls or slabs upright standing upright, not touching one another. The
heat on roasters varies as well, with hotter temps being generated in the
corners and bottom
of the pan.
Kay County Flint (Kay County, OK)
250° for 6 hrs then 50 per hr to 500° for 6 hours.
Mook Jasper (Mook Station, Australia)
250° for 8 hrs then 50 per hr to 525° for 5 hours.
Kaolin (Union Co. Ill.)
250°F for 2 hrs then 50°F/Hr to 350°F for higher grades, up
to 600°F for coarser grades. Hold at peak 6 hrs
Knife River Flint (ND)
I have had success with flakes and THIN spalls with 25°F/Hr to 350°F,
when 350°F is reached, bring down temp. 25°F/Hr. Lower grades cook
better than high grade.
A maximum of 450°F should do fine for the Moss agate. 50°F per
hour/holding at 450° for an hour or two. Don't overdue it! Try going
to 400° as a test first.
I tried cooking it first in the nodule. Many fine cracks occurred. I cook
it in slabs at 500°F. Works like obsidian and very glassy.
India Agate (bloodstone)
Treat right at 500°.Some of the more transparent is better off at 450°-480°.
Flint Ridge Chalcadony
The best grades can be worked raw. The light blue varieties are a bit tougher
and require 200° for 2 hours then bring up the temp 100 degrees an
hour till it reaches 480 degrees. Hold for two hours, shut down and allow
it to cool. Tougher varieties can be taken up to 500° for 36 to 48
Flint River Flint
Heat at 250 degrees for 2-3 hours.Increase heat 50 degrees per hour until
top temp of 375 -450°. Soak at top temp for 8 hours. Turn the device
off after the soak time and let cool.
Sunset Jasper (Richardson Ranch, Oregon)
Heat-treat at 400-425° (it gets brittle at 450+°). Don't go over
500. I have found that it's not necessary to soak it, just bring it up
slow and shut the kiln down. The yellow stone will be orange to dark red,
but this beauty is only skin deep. Some sunset has whites to purplish colors
in it.There is a sub-spiece of sunset that is yellow and appears to be
coarser in grain, though it heat-treats fine. The main difference is that
the color will penetrate all the way through. 400 = yellow, 425 = orange,
450-475 = dark red, 500 = KABOOM.
On the following materials, dry out at 200° for 8 hours,then ramp up
50° per hour
temp indicated. Hold for 8 hours. Ramp back down at 30-50° per
Kay Cnty 500-600
Ft. Hood 400-550
Edward's Plat 400-550
Montana Agate 550
Gray Boone 650
Mexcan Agate 500
Petrified Wood 300-480
Grimes Grave 400-475
Bulls Eye 450-plus
Coastal Plains 400-450
Flint Ridge 500-600
Sunset Jasper 450-475
Castroville/Uvalde cobbles 425 whole, 500 slabs
Brazilian Agate 500-600
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