Hi, (I put this little story here at "Tutorial".
Perhaps we can move it to a suitable dzial in the new layout of the forum)
I told earlier under dzial "Projekt" about a copy of the viking's Kłódka kabłąkowa I made.
However, the interesting thing is that the original locks that have been found is covered
with brass, they were lutowanie twarde with an old blacksmith's method using the palenisko !
The following story is about my try to make it again.Sources and historic use
1. The use with padlocks is thoroughly covered in http://www.archaeometry.dk/Jern/Gustafs ... rnison.pdf
It tells that most of the locks that has been found at Birka Garnison was made by this method
SEM analysis of the surface tells that e.g the surface of one lock had the composition: Cu 88.7%, Zn 11.3
Example of lock
2. Another source is "Klassiskt Järnsmide" by Karl-Gunnar Noren, ISBN 91-972615-8-0
A jolly good book with step by step description of "how to blacksmith the tools needed
for farming" It tells that krowi dzwon was often made this way in the old days.
From thin iron blacha, cut and folded to a dzwon and then lutowanie twarde to get
the nice bong---bong sound. Just a method to save expensive materials.
In the county of dalarna some smiths used this methods up to 1880. A late relative
to one of those smiths helped to describe the method in the book.
(The best detailed description I've seen yet)
3. Another source is actually the first time the method was put on paper, "De Diversis Artibus"
by the german monk Theophilius Presbyter in the 12th century. It may be considered a very
early blacksmith manual.http://en.wikipedia.org/wiki/Theophilus_Presbyter
He tells about "The brazing of iron" in Chapter XCII :
"At the point where the ironparts are to be joined, thin copper is wrapped round and
a little clay smeared round. When the clay is dry, it is put under the coals in front
of the fire and blown and, when it is red hot, the copper immediately melts and flow
round and brazes." english translation: Dodwell 1986:165 (the original was in latin)My experyment
Imagine that we have a construction with "nitowaną blachą" , that may be a
lock-house, a cow bell or something else ...
We would like to do lutowanie twarde like this
for improved strength or just for decoration.
First I made five (or six) simple ~50mm high cones of 1mm blacha like this
The ingredients to "make the cake" is (according to the book ):
1. Ceramic clay (glina)
2. Sand (piasek) I used 5% by volume of clay, my own suggestion, the recipy in the book gives no figures on that.
3. Strands of flax fibers (włókna lnianego) About half the volume of the clay (Non compressed fluffy fibers)
The filling of the iron object is made by
4. Copper (miedz) and/or Brass (mosiadz) I used small pieces, 0-10mm flakes of blacha
5. Grains of char coal (wiegel drzewny) Crushed to small pieces 0-10mm
The ingredients from start
Then I filled three cones with copper/char coal and two cones with brass/char coal.
Not shown in the picture is a chunk of clay that I put as a plunge at the
end of each cone to keep the filling in place
I added the sand to the clay and worked it well and then the flax fibers.
When the flax got in it was terrible hard to work the clay. This is because the flax
acts like arming fibers and resists every try to change the shape of the clay.
The clay-mixture was then flattened to a 20mm thick pancake and wrapped onto the cones
(Heh, now I got hungry, they looked like our swedish "bramborový knedlík" - pitepalt http://en.wikipedia.org/wiki/Pitepalt
, sorry about that ! )
This is a scetch of the final knedlik with filling
I dried the things for three weeks, first slowly in a plastic bag and
then in free air. To dry completely I used the kitchen oven at 100C for
one day or so. Sadly they got several cracks during the drying but I decided
to carry on without repairing.
Now it was time for the big try. It was 10C in the smithy that morning but
a full load of coal at maximum power changed the temperature pretty fast.
Heh, note that nice yellow sulfur fumes
getting out of the coal at the bottom-left.
I was pretty excited to carry on now and I put the first cold knedlik a little
bit too deep in the fire. The knedlik obviously got shocked and went off like a
casserolle with popcorn
The clay scattered all around and made marks like this
a sample of the grenade splitter
well, I got it out safe and put it together with a second one,
on top of the coal-pile instead. I left them like that for more than 30 minutes,
tumbling them at some instants to get an even heat from the fire.
By then they had slowly and safely been heated to above 100C and I carefully moved them
deeper and deeper into the fire. Now they were burried
As the melting point of copper is 1080C it was now crucial to get maxmimum heat
But still the temperature must be keep under the melting point of the clay.
Every 5 minutes I removed the top of the coal pile, checked the temp on the bottom side
and tumbled the knedlikis in order to move around the melted copper.
The I put the coal back again. With the coal removed it looked like this
The litterature says that thumbling should be done every minute. The total
time at full temperature should be 30 minutes for a small piece like this
(and one hour for a bigger). Though, whith koks it was impractical to carry out
this every minute, so I tried to make it move every 5 or 10 minutes instead.
This is (not the drawing of a spaceship but) the approximate dimensions during the
after 30 minutes I decided to take them out of the fire. Most critical
now is to constantly keep it tumbling on the floor. The melted miedz/mosiadz
must be evenly distributed inside and we do not now the exact time
when it freezes. At this photo the knedlik has got to rest for some 5 seconds
but it soon have to move again. Note the crack that tells that the temperature
is still quite high ~1000C
The book tells that this tumbling, actually the most important, was carried out
by the young helpers of the smith, heh
I did two in parallell and this is the second, just a little red left.
Tumble on ...
Now they are booth below 500C on the outside.
The book tells that this is the correct moment to put them in cold water.
But why ? The book says that if it's left in the air to cool the
miedz/mosiadz will get a blue/green oxide layer. So putting in the water
when it's still hot is important. The smiths helpers got slapped on their butts
if they forgot and as further punishment they had to rub away the oxide by hand.
Now it's cold and cool.
- Really sad to break it
Had to break it.
... not much of copper on the outside
Just a little on the tip. Barely visible on the photo.
(If you see yellow stuff elsewhere it's probably oxides)
Half a success, the copper has melted and cover 100% of the inside
Time to open number 2 ...
95% of the outside is covered with copper. It seems to be bright
yellow in colour on the photo but it's actually copper-red (bad lamp in my smithy >
false colours on my photos)
The joints of the blachas ends are nicely filled with copper - better than
if I had done with modern gas equipment.
Still there is more copper on the inside. (Perhaps I was too lazy with
that important tumbling when it was still hot). The last 5mm of the joint
was filled with clay and the copper had no chance to fill this space.
Now I polished the two cones and I got quite happy with the second. It has
a clear and high-pitch pling-sound when hitting it with a screwdriver.
(Would have been a nice bong---boong with a bigger krowi dzwon)
Then I did the last three together in the palensiko, probably a mistake because when I cracked
the first one I saw that the copper had not been melted. Not enough heat
Mistakes are for learning ... I did not break the other two. Instead I got them
back to the palenisko at maximum heat (+ a little more
Puuh, now the experyment was completed and the result looked like thisSummary
No1 Copper Melted nice on inside but only 5% outside cover
No2 Copper Nice - 100% inside - 95% outside
No3 Copper Didn't melt, not enough heat
No4 Brass Nice - 100% inside - 95% outside, Zn burnt away as ZnO, only copper left I think
No5 Brass Nice - 100% inside - 95% outside, Zn burnt away as ZnO, only copper left Some conclutions I made1
Use MUCH HEAT. The book tells that the smiths learned what the clay-surface
should look like when the "knedlik" was ready.
With no 3 the clay did not change on the surface, only a darker
colour - and the copper did not melt. With no 5 I used a tremendous amount of heat, the clay-surface
converted to glass-like and the koks got stuck to it. The result was very good.
With a normal palenisko it's impossible to use to much heat I think - go for maximum ! 2
Using copper is much easier than using brass. With copper some cracks in the clay was
not critical. With brass, the smallest crack in the clay caused the zink to escape and burn to ZnO.
After I had done no 4 & 5 I found some very white koks (with ZnO) on top of the palenisko,
the things to the right in the picture. Not very healty, my life probably got
shortened some weeks (or years
) or so. 3
None of the steps in the process was difficult to do. It uses only simple ingredients and
a lot of work. For a start it's always possible to try the fast n easy one: Heat a blacha
covered with borax in the palenisko, apply copper wire (from a silnik or transformator)
when blacha is more than 1000C. Works pretty well and it often gives "arty" oxide colours
on the copper surface.
I recommend an experiment with this method, it's fun
- - -
In the next step I'd like to do some "real thing" out of blacha and put copper on it. Making a
padlock is far to much work if it gets spoiled but don't get surprised if a krowi dzwon pops up
here shortly. Yea, I think I make such'a dzwon ...