Rasjid and Jean.
Iron and steel are both ferric material.
The difference between iron and steel is that pure iron does not contain carbon, steel does contain carbon.
Pure iron, i.e., ferric material that does not contain carbon or other impurities, is very soft, and because it does not contain carbon, it cannot be hardened.
When ferric material contains too much carbon, that very high content of carbon --- say, above 1.2%--- must be reduced to a level that permits the ferric material to be hardened to a degree that is sufficiently hard for work, but not brittle. This cleansing process in South East Asia was carried out by the repeated folding and welding of the ferric material to remove the excess carbon. In Jawa this is known as "washing the iron". In practice, the material is repeatedly folded and welded until sparks do not rise from a billet at weld heat when that billet is struck with a hammer.
For ferric material to become sufficiently hard to be used for tools that are required to hold an edge, and not break because of brittleness, the carbon content should be between +/- .4 % and +/- 1.2% . For example, a very useful modern simple carbon steel is 01 :- oil hardening steel with 1% carbon.
After steel has been hardened by heating to its critical temperature and quenched in the appropriate medium, it is hard, but it is also brittle, and that brittleness needs to be reduced. This is done by heating the steel to a temperature below critical, indicated by a heat produced colour band on the steel and then quenched to hold the steel at the degree of hardness indicated by the colour band.
Although Jawa did and does have sources of iron ore, mostly contained in beach sands, it seems that the iron produced from these sources was of a low quality and that it contained a high percentage of phosphorus, an impurity which causes iron to be very brittle. High phosphorus irons are usually lighter in colour than most other irons.
In Maritime S.E. Asia the Iron Age and the Bronze Age seem to have arrived at approximately the same time and to have progressed together. This very probably occurred because both iron and bronze were introduced to Maritime S.E. Asia by trade originating from other countries, notably China and the Indian Sub-Continent.
In Jawa the sources of iron used were principally imports from China and India in the early years of the first millennium, and later from Europe, China and India after European contact. Thus, although Jawa did have its own iron, it was more practical to use the iron imported from other countries, and this imported iron appears to have been mixed by the forge welding process with the local high phosphorus iron, thus producing mixed iron, which was called "pamor". Use of this mixing technique had two very useful factors, firstly it extended the quantity of the expensive imported iron and secondly it produced a product that had a high degree of resistance to breaking, however, this material was not able to hold a cutting edge for long, so a wafer of steel was inserted into the blade to produce an edge that could be hardened. There were several methods used to insert this wafer of steel.
When iron is produced from iron ore by smelting , the resultant product is called "pig iron", or "cast iron". This is very brittle and contains a number of impurities including carbon. The most primitive form of smelting is by use of a bloomery, which produces a "bloom" of very dirty sponge iron. The pig iron, and the sponge iron is then refined to produce wrought iron. Useable steel can be produced by working bloomery iron or cast iron to a degree sufficient to leave a low carbon content, or by producing carbon free wrought iron and then reintroducing carbon to that wrought iron.
These processes have around for about 4000 years.
So, although the modern, industrialised production of steel with varying degrees of carbon content is a comparatively recent occurrence, mankind has been able to produce iron and steel with varying degrees of carbon content for a very long time indeed.
When steel has been heat treated to make it hard, the quenching process leaves a signature in the material:- the hardened section of the material is darker in colour than the unhardened section.
To address your specific question Rasjid. All three of these blades are iron blades. I think it is possible that at least a part of the edges might have had carbon introduced by the case hardening method, however it is now impossible to know that with any certainty, because case hardening results in only a very shallow penetration of carbon to the iron, and erosion has removed any evidence of this.
|