slab to stab tutorial - jim winn 2004

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Slab to Stab

A Jim Winn

Tutorial

By Custom Imprints by Lee Parker

[email protected]

Copyright 2004 Jim Winn


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December 27, 2003

The following text describes the method I used to produce a large blade from a slab of

obsidian. I took a series of 24 photos in sequence showing the process of making the

blade from start to finish. The photos are named P01 thru P24. There are many strategys

that can be used to work a slab into a blade. The normal approach is to create convexityon both faces after removing the square edges. This works well on smaller slabs. On large

wide slabs, however, it can be a problem to remove the saw marks on the center of the

faces when using pressure flaking. If the slab is or thicker, I normally use percussion

to remove the saw marks and create a bi-face. On thinner large slabs, however, there is

too great of a risk of breaking the slab using percussion to remove the saw marks. This is

when the Ishi stick can be used very effectively. But, instead of creating convexity first, I

try to remove all traces of the saw marks on the first pressure flaking pass, and then

create the convexity on the 2nd pressure flaking pass. The reason for this is that flakes

travel further on a flat surface than on curved surface for a given amount of applied force.As the convexity is increased (the curvature of the face), the distance the flake will travel

becomes less. This assumes that nothing is in contact with the flake as it is being

released. Some knappers have good success using a soft leather pad to increase flake

travel over a curved surface, but I have never mastered that technique. When trying to

remove saw marks after convexity has been created, it is easy to leave islands of saw

marks that can be really frustrating to reach. OK, here we go.

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P1 This pic shows the slab of obsidian I started with. The piece came from the

Needles pit at Davis creek California and was collected last September . It was one of

many large chunks discarded by Needles miners. I used an 18 gravity feed saw to cut the

slab in roughly 15 minutes. The slab is 12 X 4 by 9/16 thick. Also included in the pic

are the various tools used to make the blade. On the left are 2 solid copper bars used for

percussion flaking the edge. Above are 2 Ishi sticks used for the pressure flaking. Below

are the hand pads used to support the blade. Also a piece of leather used below the pad to

provide further protection from cuts. On the right is part of a grinding wheel used to

abrade the platforms.

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P2 The square edges of the slab need to be removed to create a workable platform for

further pressure flaking. This pic demonstrates alternate beveling using a small solid

copper bar for percussion flaking the square edge. The slab is held on the padded legwith the area to be struck in firm contact with the leg. This allows the shock to be

absorbed by the leg and reduces the risk of breaking the slab. A flake is removed by

striking gently almost straight down and a bit forward. The pic shows the correct area to

strike. The slab is then flipped over and another flake struck on the edge just produced by

the previous flake. Grinding is not needed at this stage. This continues around the entire

slab, so long as the edge is roughly square. Pass over areas with sharper edges, andcontinue when the edge becomes square. Be extra careful when working the ends or the

slab may break. Switch to using an Ishi stick for alternate beveling whenever there is

concern of breakage. The Ishi stick works great for this, just takes more time.

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P3 Another photo showing the point of contact from a different perspective. Note

how the small diameter bar fits nicely against the edge of the previous flake. Larger

diameter copper can be used for this, but there is greater risk of breakage.

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P4 This pic shows how to deal with edges that are not square. The edge angle here is

about 45 degrees, so I just removed about 3 flakes in a row on the same face until the

edge angle returned to a square edge, and then continued with alternate flaking again.

5


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P5 Edging is now complete. The edge angle varies but is roughly 40-80 degrees and

within 1/8 or so of the center plane. I did not edge the right end as this will be done

when shaping.

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P6 The next step is to roughly shape the blade and create symmetry beforeattempting to pressure flake the faces. The first step is to determine which edges of the

slab need to be trimmed. Then I strike these edges with the side of the copper bar while

sliding the bar downward along the slab edge. This is done rapidly and repeatedly along

the edge to prepare platforms. This is kind of hard to explain, but what happens is that

very small flakes are removed which brings the edge of the platform closer to the face

that is seen in the pic. Its just a quick way to raise the platform edge closer to the face.

Sort of abrading and flaking at the same time. Then the slab is flipped over and short

flakes are struck off to bring the edge in to provide symmetry. If more needs to be

trimmed off, the slab edge is abraded with the edge of the copper bar again, flipped over,and additional flakes are removed.

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P7 The slab has now been roughly shaped. The next step is to create a good solid

platform along the entire edge to prepare it for pressure flaking. The face shown is the

face that will be pressure flaked first (face A). To get the flakes to travel the greatest

distance over this face and remove as much of the saw marks as possible the platform

needs to be about 1/8 below the face of this slab. If the platform is deeper (closer to the

center plane), the pressure flakes will require too much force to initiate fracture and

typically they will not travel as far. If the platform is too shallow (1/16 or less), the

pressure flake will be too thin and will often break in a small step before traveling very

far.

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P8 This shows the platform ready for pressure flaking. This platform was made usingthe solid copper bar by removing small flakes along the edge as needed to bring the edge

up to within 1/8 or so of the face. It was then abraded with the grinding stone. This

platform is actually not as straight as it should have been I would have been better off

straightening it a bit with the Ishi stick.

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P9 This pic shows the flakes to be removed with the Ishi stick on face A. I started at

the tip and worked backward toward the base. The idea is to remove a long flake, then a

short flake to straighten the ridge for the next long flake to follow. Then another longflake, followed by another short flake to straighten the next ridge and so on. Long flake,

short flake, long flake, short flake, all the way to the base.

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P10 This pic shows the first 7 long flakes that were removed with the Ishi stick on faceA. Note: between each of these flakes a small flake was removed sequentially.

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P11 This pic shows the tip of the Ishi stick in the proper position and at the proper

contact point to initiate the next long flake. Note that the tip of the pressure flaker is

actually pointing toward the back face a little, in other words more than straight in. This

allows a maximum amount of force to be built up before the flake releases. If the tip of

the pressure flaker is pointing straight in the flake may release too soon and not travel as

far as intended. Also note that the tip of the pressure flaker in not too sharp and that it is

5/16 diameter copper. Thinner copper may bend. It the tip is filed too sharp, the flake

may release before sufficient pressure is built up, and again a short flake may result. One

last note is that my Ishi sticks are re-inforced with carbon fiber and epoxy which keepsthe ends from splitting. You can get carbon fiber at any hobby shop.

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P12 This shows the typical holding position using the Ishi stick.

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P13 A closer pic showing the Ishi stick ready to remove a long flake. Again, notice

how the tip of the stick is pointing slightly toward the back of the slab face. Once I have

reached the maximum amount of force I am capable of, I give everything a slight jerk to

further increase the amount of applied force and release the flake. At the same moment,

my left hand rotates just slightly allowing the force of the tip to be directed more straight

in. My right hand holding the Ishi stick changes the direction of applied force slightly

toward the face to be flaked, thus initiating the flake release. The flake must release

directly below the notch in the rubber hand pad. It the flake releases where it makes

contact with the pad it will terminate at that spot in a small step.

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P14 This pic explains the importance of removing a small flake after each large flake

to straighten the ridge for the next flake to follow. This is similar to the guide flakes used

to prepare nipple platforms on Clovis performs. The main difference is that the platform

is prepared on one side only.

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P15 This face has now been flaked along one entire side of the face (face A). Most ofthe flakes traveled more than half way to the opposite edge. This makes the job of

removing the remaining saw marks much easier when flaking the opposite edge.

However, prior to pressure flaking the opposite edge, I prefer to pressure flake the

opposite edge of the opposite face (face B).

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P16 Face B has been pressure flaked along one entire edge. Note that I got a little

sloppy here and some of the flakes did not travel to the mid point of the face. This is

mainly the result of poor platform preparation. This will make things more difficult later

on!

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P17 Another platform has been created to remove pressure flakes from the oppositeedge on face A. I took a little greater care in preparing this platform to insure that the

flakes travel well. I used an Ishi stick to get it as straight as possible and ground it well.

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P18 This is face A with one set of pressure flakes removed along both edges. No saw

marks remain. So far, so good

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P19 Another platform has been prepared to pressure flake the opposite edge of face B.

Some of these flakes are going to have to travel a long distance to remove all the saw

marks!

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P20 Well, almost made it! One small Island of saw marks remains on face B near the

center. Bummer! This will require that the right side edge be beveled back toward face A

to remove a 2nd

set of flakes along this edge and attempt to remove the island.

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P21 Success! The 2nd

pass undercut the island and also added additional convexity on

face B, which previously was very flat. Finishing up the blade is now easy. Face B has a

good flaking pattern and good symmetry and needs no further attention. Face A,

however, is still too flat. Also, the blade needs minor adjustment in shaping. The blade is

finished by removing a series of pressure flakes along both edges of face A using an

ordinary hand pressure flaker. These flakes on average are traveling only about 1 or so

and the hand flaker gives more control than the Ishi stick. The goal is to provide a nice

sharp edge that is straight and add some curvature to the face as well.

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P22 This pic shows the completed blade, face B.

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P23 This pic shows the completed blade, face A.

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P24 This pic shows the completed blade as viewed from the edge. The finished blade

is 11 long, by 2 wide, by 7/16 thick. Total time to make the blade: About 3

hours (not counting the time to take the pics).

Hope this is of some help.Jim Winn

slab to stab tutorial - jim winn 2004

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