More manual

Added sections on the technic-specific kinds of item processing, and on
generic metal mechanics, and the specific trickery around iron (merging
in notes_on_iron).

manual.md

@@ -160,12 +160,274 @@ elevation -150 downwards.  It is much harder to dig than standard stone,
 so impedes mining when it is encountered.  It has mainly decorative use,
 but also appears in a couple of machine recipes.
 
+alloying
+--------
+
+In technic, alloying is a way of combining items to create other items,
+distinct from standard crafting.  Alloying always uses inputs of exactly
+two distinct types, and produces a single output.  Like cooking, which
+takes a single input, it is performed using a powered machine, known
+generically as an "alloy furnace".  An alloy furnace always has two
+input slots, and it doesn't matter which way round the two ingredients
+are placed in the slots.  Many alloying recipes require one or both
+slots to contain a stack of more than one of the ingredient item: the
+quantity required of each ingredient is part of the recipe.
+
+As with the furnaces used for cooking, there are multiple kinds of alloy
+furnace, powered in different ways.  The most-used alloy furnaces are
+electrically powered.  There is also an alloy furnace that is powered
+by directly burning fuel, just like the basic cooking furnace.  Building
+almost any electrical machine, including the electrically-powered alloy
+furnaces, requires a machine casing component, one ingredient of which
+is brass, an alloy.  It is therefore necessary to use the fuel-fired
+alloy furnace in the early part of the game, on the way to building
+electrical machinery.
+
+Alloying recipes are mainly concerned with metals.  These recipes
+combine a base metal with some other element, most often another metal,
+to produce a new metal.  This is discussed in the section on metal.
+There are also a few alloying recipes in which the base ingredient is
+non-metallic, such as the recipe for the silicon wafer.
+
+grinding, extracting, and compressing
+-------------------------------------
+
+Grinding, extracting, and compressing are three distinct, but very
+similar, ways of converting one item into another.  They are all quite
+similar to the cooking found in the basic Minetest game.  Each uses
+an input consisting of a single item type, and produces a single
+output.  They are all performed using powered machines, respectively
+known generically as a "grinder", "extractor", and "compressor".
+Some compressing recipes require the input to be a stack of more than
+one of the input item: the quantity required is part of the recipe.
+Grinding and extracting recipes never require such a stacked input.
+
+There are multiple kinds of grinder, extractor, and compressor.  Unlike
+cooking furnaces and alloy furnaces, there are none that directly burn
+fuel; they are all electrically powered.
+
+Grinding recipes always produce some kind of dust, loosely speaking,
+as output.  The most important grinding recipes are concerned with metals:
+every metal lump or ingot can be ground into metal dust.  Coal can also
+be ground into dust, and burning the dust as fuel produces much more
+energy than burning the original coal lump.  There are a few other
+grinding recipes that make block types from the basic Minetest game
+more interconvertible: standard stone can be ground to standard sand,
+desert stone to desert sand, cobblestone to gravel, and gravel to dirt.
+
+Extracting is a miscellaneous category, used for a small group
+of processes that just don't fit nicely anywhere else.  (Its name is
+notably vaguer than those of the other kinds of processing.)  It is used
+for recipes that produce dye, mainly from flowers.  (However, for those
+recipes using flowers, the basic Minetest game provides parallel crafting
+recipes that are easier to use and produce more dye, and those recipes
+are not suppressed by technic.)  Its main use is to generate rubber from
+raw latex, which it does three times as efficiently as merely cooking
+the latex.  Extracting was also formerly used for uranium enrichment for
+use as nuclear fuel, but this use has been superseded by a new enrichment
+system using the centrifuge.
+
+Compressing recipes are mainly used to produce a few relatively advanced
+artificial item types, such as the copper and carbon plates used in
+advanced machine recipes.  There are also a couple of compressing recipes
+making natural block types more interconvertible.
+
+centrifuging
+------------
+
+Centrifuging is another way of using a machine to convert items.
+Centrifuging takes an input of a single item type, and produces outputs
+of two distinct types.  The input may be required to be a stack of
+more than one of the input item: the quantity required is part of
+the recipe.  Centrifuging is only performed by a single machine type,
+the MV (electrically-powered) centrifuge.
+
+Generally, centrifuging separates the input item into constituent
+substances, but it can only work when the input is reasonably fluid,
+and in marginal cases it is quite destructive to item structure.
+(In real life, centrifuges require their input to be mainly fluid, that
+is either liquid or gas.  Few items in the game are described as liquid
+or gas, so the concept of the centrifuge is stretched a bit to apply to
+finely-divided solids.)
+
+The main use of centrifuging is in uranium enrichment, where it
+separates the isotopes of uranium dust that otherwise appears uniform.
+Enrichment is a necessary process before uranium can be used as nuclear
+fuel, and the radioactivity of uranium blocks is also affected by its
+isotopic composition.
+
+A secondary use of centrifuging is to separate the components of
+metal alloys.  This can only be done using the dust form of the alloy.
+It recovers both components of binary metal/metal alloys.  It can't
+recover the carbon from steel or cast iron.
+
+metal
+-----
+
+Many of the substances important in technic are metals, and there is
+a common pattern in how metals are handled.  Generally, each metal can
+exist in five forms: ore, lump, dust, ingot, and block.  With a couple of
+tricky exceptions in mods outside technic, metals are only *used* in dust,
+ingot, and block forms.  Metals can be readily converted between these
+three forms, but can't be converted from them back to ore or lump forms.
+
+As in the basic Minetest game, a "lump" of metal is acquired directly by
+digging ore, and will then be processed into some other form for use.
+A lump is thus more akin to ore than to refined metal.  (In real life,
+metal ore rarely yields lumps ("nuggets") of pure metal directly.
+More often the desired metal is chemically bound into the rock as an
+oxide or some other compound, and the ore must be chemically processed
+to yield pure metal.)
+
+Not all metals occur directly as ore.  Generally, elemental metals (those
+consisting of a single chemical element) occur as ore, and alloys (those
+consisting of a mixture of multiple elements) do not.  In fact, if the
+fictional mithril is taken to be elemental, this pattern is currently
+followed perfectly.  (It is not clear in the Middle-Earth setting whether
+mithril is elemental or an alloy.)  This might change in the future:
+in real life some alloys do occur as ore, and some elemental metals
+rarely occur naturally outside such alloys.  Metals that do not occur
+as ore also lack the "lump" form.
+
+The basic Minetest game offers a single way to refine metals: cook a lump
+in a furnace to produce an ingot.  With technic this refinement method
+still exists, but is rarely used outside the early part of the game,
+because technic offers a more efficient method once some machines have
+been built.  The grinder, available only in electrically-powered forms,
+can grind a metal lump into two piles of metal dust.  Each dust pile
+can then be cooked into an ingot, yielding two ingots from one lump.
+This doubling of material value means that you should only cook a lump
+directly when you have no choice, mainly early in the game when you
+haven't yet built a grinder.
+
+An ingot can also be ground back to (one pile of) dust.  Thus it is always
+possible to convert metal between ingot and dust forms, at the expense
+of some energy consumption.  Nine ingots of a metal can be crafted into
+a block, which can be used for building.  The block can also be crafted
+back to nine ingots.  Thus it is possible to freely convert metal between
+ingot and block forms, which is convenient to store the metal compactly.
+Every metal has dust, ingot, and block forms.
+
+Alloying recipes in which a metal is the base ingredient, to produce a
+metal alloy, always come in two forms, using the metal either as dust
+or as an ingot.  If the secondary ingredient is also a metal, it must
+be supplied in the same form as the base ingredient.  The output alloy
+is also returned in the same form.  For example, brass can be produced
+by alloying two copper ingots with one zinc ingot to make three brass
+ingots, or by alloying two piles of copper dust with one pile of zinc
+dust to make three piles of brass dust.  The two ways of alloying produce
+equivalent results.
+
+iron and its alloys
+-------------------
+
+Iron forms several important alloys.  In real-life history, iron was the
+second metal to be used as the base component of deliberately-constructed
+alloys (the first was copper), and it was the first metal whose working
+required processes of any metallurgical sophistication.  The game
+mechanics around iron broadly imitate the historical progression of
+processes around it, rather than the less-varied modern processes.
+
+The two-component alloying system of iron with carbon is of huge
+importance, both in the game and in real life.  The basic Minetest game
+doesn't distinguish between these pure iron and these alloys at all,
+but technic introduces a distinction based on the carbon content, and
+renames some items of the basic game accordingly.
+
+The iron/carbon spectrum is represented in the game by three metal
+substances: wrought iron, carbon steel, and cast iron.  Wrought iron
+has low carbon content (less than 0.25%), resists shattering, and
+is easily welded, but is relatively soft and susceptible to rusting.
+In real-life history it was used for rails, gates, chains, wire, pipes,
+fasteners, and other purposes.  Cast iron has high carbon content
+(2.1% to 4%), is especially hard, and resists corrosion, but is
+relatively brittle, and difficult to work.  Historically it was used
+to build large structures such as bridges, and for cannons, cookware,
+and engine cylinders.  Carbon steel has medium carbon content (0.25%
+to 2.1%), and intermediate properties: moderately hard and also tough,
+somewhat resistant to corrosion.  In real life it is now used for most
+of the purposes previously satisfied by wrought iron and many of those
+of cast iron, but has historically been especially important for its
+use in swords, armour, skyscrapers, large bridges, and machines.
+
+In real-life history, the first form of iron to be refined was
+wrought iron, which is nearly pure iron, having low carbon content.
+It was produced from ore by a low-temperature furnace process (the
+"bloomery") in which the ore/iron remains solid and impurities (slag)
+are progressively removed by hammering ("working", hence "wrought").
+This began in the middle East, around 1800 BCE.
+
+Historically, the next forms of iron to be refined were those of high
+carbon content.  This was the result of the development of a more
+sophisticated kind of furnace, the blast furnace, capable of reaching
+higher temperatures.  The real advantage of the blast furnace is that it
+melts the metal, allowing it to be cast straight into a shape supplied by
+a mould, rather than having to be gradually beaten into the desired shape.
+A side effect of the blast furnace is that carbon from the furnace's fuel
+is unavoidably incorporated into the metal.  Normally iron is processed
+twice through the blast furnace: once producing "pig iron", which has
+very high carbon content and lots of impurities but lower melting point,
+casting it into rough ingots, then remelting the pig iron and casting it
+into the final moulds.  The result is called "cast iron".  Pig iron was
+first produced in China around 1200 BCE, and cast iron later in the 5th
+century BCE.  Incidentally, the Chinese did not have the bloomery process,
+so this was their first iron refining process, and, unlike the rest of
+the world, their first wrought iron was made from pig iron rather than
+directly from ore.
+
+Carbon steel, with intermediate carbon content, was developed much later,
+in Europe in the 17th century CE.  It required a more sophisticated
+process, because the blast furnace made it extremely difficult to achieve
+a controlled carbon content.  Tweaks of the blast furnace would sometimes
+produce an intermediate carbon content by luck, but the first processes to
+reliably produce steel were based on removing almost all the carbon from
+pig iron and then explicitly mixing a controlled amount of carbon back in.
+
+In the game, the bloomery process is represented by ordinary cooking
+or grinding of an iron lump.  The lump represents unprocessed ore,
+and is identified only as "iron", not specifically as wrought iron.
+This standard refining process produces dust or an ingot which is
+specifically identified as wrought iron.  Thus the standard refining
+process produces the (nearly) pure metal.
+
+Cast iron is trickier.  You might expect from the real-life notes above
+that cooking an iron lump (representing ore) would produce pig iron that
+can then be cooked again to produce cast iron.  This is kind of the case,
+but not exactly, because as already noted cooking an iron lump produces
+wrought iron.  The game doesn't distinguish between low-temperature
+and high-temperature cooking processes: the same furnace is used not
+just to cast all kinds of metal but also to cook food.  So there is no
+distinction between cooking processes to produce distinct wrought iron
+and pig iron.  But repeated cooking *is* available as a game mechanic,
+and is indeed used to produce cast iron: re-cooking a wrought iron ingot
+produces a cast iron ingot.  So pig iron isn't represented in the game as
+a distinct item; instead wrought iron stands in for pig iron in addition
+to its realistic uses as wrought iron.
+
+Carbon steel is produced by a more regular in-game process: alloying
+wrought iron with coal dust (which is essentially carbon).  This bears
+a fair resemblance to the historical development of carbon steel.
+This alloying recipe is relatively time-consuming for the amount of
+material processed, when compared against other alloying recipes, and
+carbon steel is heavily used, so it is wise to alloy it in advance,
+when you're not waiting for it.
+
+There are additional recipes that permit all three of these types of iron
+to be converted into each other.  Alloying carbon steel again with coal
+dust produces cast iron, with its higher carbon content.  Cooking carbon
+steel or cast iron produces wrought iron, in an abbreviated form of the
+bloomery process.
+
+There's one more iron alloy in the game: stainless steel.  It is managed
+in a completely regular manner, created by alloying carbon steel with
+chromium.
+
 subjects missing from this manual
 ---------------------------------
 
 This manual needs to be extended with sections on:
 
-*   alloying
+*   rubber
 *   electrical networks
 *   the powered machine types
 *   how machines interact with tubes

notes_on_iron

@@ -1,68 +0,0 @@
-Notes on iron and steel
-=======================
-
-Alloying iron with carbon is of huge importance, but in some processes
-the alloying is an implicit side effect rather than the product of
-explicit mixing, so it is a complex area.  In the real world, there is
-a huge variety of kinds of iron and steel, differing in the proportion
-of carbon included and in other elements added to the mix.
-
-The Minetest default mod doesn't distinguish between types of iron and
-steel at all.  This mod introduces multiple types in order to get a bit
-of complexity and flavour.
-
-Leaving aside explicit addition of other elements, the iron/carbon
-spectrum is here represented by three substances: wrought iron,
-carbon steel, and cast iron.  Wrought iron has low carbon content
-(less than 0.25%), resists shattering, and is easily welded, but is
-relatively soft and susceptible to rusting.  It was used for rails,
-gates, chains, wire, pipes, fasteners, and other purposes.  Cast iron
-has high carbon content (2.1% to 4%), is especially hard, and resists
-corrosion, but is relatively brittle, and difficult to work.  It was used
-to build large structures such as bridges, and for cannons, cookware,
-and engine cylinders.  Carbon steel has medium carbon content (0.25%
-to 2.1%), and intermediate properties: moderately hard and also tough,
-somewhat resistant to corrosion.  It is now used for most of the purposes
-previously satisfied by wrought iron and many of those of cast iron,
-but has historically been especially important for its use in swords,
-armour, skyscrapers, large bridges, and machines.
-
-Historically, the first form of iron to be refined was wrought iron,
-produced from ore by a low-temperature furnace process in which the
-ore/iron remains solid and impurities (slag) are progressively removed.
-Cast iron, by contrast, was produced somewhat later by a high-temperature
-process in a blast furnace, in which the metal is melted, and carbon is
-unavoidably incorporated from the furnace's fuel.  (In fact, it's done
-in two stages, first producing pig iron from ore, and then remelting the
-pig iron to cast as cast iron.)  Carbon steel requires a more advanced
-process, in which molten pig iron is processed to remove the carbon,
-and then a controlled amount of carbon is explicitly mixed back in.
-Other processes are possible to refine iron ore and to adjust its
-carbon content.
-
-Unfortunately, Minetest doesn't let us readily distinguish between
-low-temperature and high-temperature processes: in the default game, the
-same furnace is used both to cook food (low temperature) and to cast metal
-ingots (varying high temperatures).  So we can't sensibly have wrought
-iron and cast iron produced by different types of furnace.  Nor can
-furnace recipes discriminate by which kind of fuel is used (and thus
-by the availability of carbon).  The alloy furnace allows for explicit
-alloying, which appropriately represents how carbon steel is made, but
-is not sensible for the other two, and is a relatively advanced process.
-About the only option to make a second iron-processing furnace process
-readily available is to cook multiple times; happily, this bears a slight
-resemblance to the real process with pig iron as an intermediate product.
-
-The default mod's refined iron, which it calls "steel", is identified
-with this mod's wrought iron.  Cooking an iron lump (representing ore)
-initially produces wrought iron; the cooking process here represents a
-low-temperature bloomery process.  Cooking wrought iron then produces
-cast iron; this time the cooking process represents a blast furnace.
-Alloy cooking wrought iron with coal dust (carbon) produces carbon steel;
-this represents the explicit mixing stage of carbon steel production.
-Additionally, alloy cooking carbon steel with coal dust produces cast
-iron, which is logical but not very useful.  Furthermore, to make it
-possible to turn any of the forms of iron into any other, cooking carbon
-steel or cast iron produces wrought iron, in an abbreviated form of the
-bloomery process.  As usual for metals, the same cooking and alloying
-processes can be performed in parallel forms on ingots or dust.