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[LegoLord]

It's not going to set a goblin on fire, though, or heat steel enough for forging. Might cook a meal.

It's all about scale. A two by three sheet of plywood can cook a meal. A 20 by 30 foot array lights a goblin on fire. A 50 foot square array forges steel. These are dwarves, creating a giant solar death array seems like the sort of thing that they would do. I'd personally use silver for the mirror material, but bronze might work as well..

Doesn't quite work like that.  One, where on earth would they get that much metal?  Two, the latter would melt itself; if it were even possible.  You can't achieve temperatures like that with mere sunlight; it's just not a thermodynamically sound concept.

[profit]

It's not going to set a goblin on fire, though, or heat steel enough for forging. Might cook a meal.

It's all about scale. A two by three sheet of plywood can cook a meal. A 20 by 30 foot array lights a goblin on fire. A 50 foot square array forges steel. These are dwarves, creating a giant solar death array seems like the sort of thing that they would do. I'd personally use silver for the mirror material, but bronze might work as well..

Doesn't quite work like that.  One, where on earth would they get that much metal?  Two, the latter would melt itself; if it were even possible.  You can't achieve temperatures like that with mere sunlight; it's just not a thermodynamically sound concept.

Although this solar oven business is (no pun intended) shady...  the temprature level is achievable with sunlight.

http://pr-project.blogspot.com/2008/10/solar-furnace-melts-steel-amazingly.html

[Rysith]

Doesn't quite work like that.  One, where on earth would they get that much metal?  Two, the latter would melt itself; if it were even possible.  You can't achieve temperatures like that with mere sunlight; it's just not a thermodynamically sound concept.

The metal wouldn't melt any more than any other piece of metal would melt, because you aren't heating the surface of the metal.

Achieving those temperatures with "mere sunlight" is perfectly thermodynamically feasible: you're taking the hundreds of watts/m^2 of sunlight that you get, and focusing it onto a much smaller area. See here for some demonstrations with a 2x3 lens. I'd claim that, even accounting for inefficiencies from using silver (as opposed to say, gold and its 99%+ reflectivity), dwarves could easily gather enough metal for a mirror that would be well more than capable of forging and lighting things on fire.

[Neonivek]

Well... Snow reflects 90% of sunlight (or some other high number) so I guess a Solar Furnace could be created from Snow.

This is of course ignoring the naturally occuring Phenomona where the Sun just randomly bakes a location in intense heat for seemingly no reason.

[G-Flex]

Well... Snow reflects 90% of sunlight (or some other high number) so I guess a Solar Furnace could be created from Snow.

Except snow scatters the light, making it unusable.

[FoboslC]

Weapons? naaah, absolutely useless and pointless bullcrap.
Cooking? Yeah, leaving pice of meat under scroching sun on th stone to cook it? Nice, I'd use that

[LegoLord]

The metal wouldn't melt any more than any other piece of metal would melt, because you aren't heating the surface of the metal.

But you are heating the air inside of it, which touches the metal.  So eventually, yes, this will melt it, seeing as how most metals used for mirrors in the dwarves time frame have fairly low melting points.    In 1400, they did not have the knowledge or tools to create something precise enough to reach those temperatures.  Also, metals are good conductors of heat (so a lot heat would radiate through the metal mirrors) , whereas glass is not, meaning glass would be more effective at focusing the heat (assuming it could be made properly, which they couldn't back then). 

I should also point out that it is only 1000 watts per directly exposed square meter (big space), which is frequently unavailable in certain climates.  There's still quite a lot, just not quite so much as it would initially appear.

[profit]

The metal wouldn't melt any more than any other piece of metal would melt, because you aren't heating the surface of the metal.

But you are heating the air inside of it, which touches the metal.  So eventually, yes, this will melt it, seeing as how most metals used for mirrors in the dwarves time frame have fairly low melting points.    In 1400, they did not have the knowledge or tools to create something precise enough to reach those temperatures.  Also, metals are good conductors of heat (so a lot heat would radiate through the metal mirrors) , whereas glass is not, meaning glass would be more effective at focusing the heat (assuming it could be made properly, which they couldn't back then). 

I should also point out that it is only 1000 watts per directly exposed square meter (big space), which is frequently unavailable in certain climates.  There's still quite a lot, just not quite so much as it would initially appear.

(This is still not dwarven tech level appropriate but I feel the need to comment)

Do cars melt?  Do mirrors outside melt?   The mirrors themselves do not get hot, they reflect the infrared rays onto a focal point but themselves do not get hot.

It is the place focused on that has to be able to take the heat.   This would have to be made out of high temprature ceramics and such (even then it might not be able to take the heat)  If the focus point is 20 feet from the mirrors themselves or more the mirrors would feel no heat from the air, and would themselves not get hot.

Polished metals like silver and gold do an excellent job of reflecting infrared, so in theory they could build the mirrors. 

The watts per meter isnt really too much of an issue, you only need maybe 750 watts to melt metal if it is focused at all,  heck you could melt lead with a really well focused 50 watts, and with mirrors you can get far above a single square meter.

The only issue holding dwarves back that I can see would be the inability to create perfectly flat mirrors. 

If they could make perfectly flat mirrors they could do this.. BUT it is far out of their tech level to do so.

I don't quite think you are quite getting what a solar furnace is so here have a look.  See how the mirrors are not the part that gets hot. It is the place the light is focused to.

Spoiler (click to show/hide)

Here is another image of a solar furnace in operation See how the mirrors are about 10 meters (30+ feet) from the focus point.

Spoiler (click to show/hide)

*Still feasibility aside, this IS NOT period appropriate. Certainly not for dwarves who hole up in mountains.

[LegoLord]

As far as the mirror heating goes:

You have the focal point.  It is very hot.

You have the air between it and the mirror.  It is significantly cooler.

The heat moves out through the air and into it's surroundings (including the mirror), because heat tends to leave hot objects if there is a cooler object to take the heat.

[profit]

As far as the mirror heating goes:

You have the focal point.  It is very hot.

You have the air between it and the mirror.  It is significantly cooler.

The heat moves out through the air and into it's surroundings (including the mirror), because heat tends to leave hot objects if there is a cooler object to take the heat.

The air between the mirrors and the object is a massive resistance though, and it just works. In Real life it does not melt the mirrors, They even used Dorito bags for solar furnaces and they work.

Just trust me on this, 40 feet of air provides a massive amount of resistance to heat.  You can place your hand above a one thousand degree pan at the distance of a few inches and not have your blood boiled away, now make that distance a hundred times further, and have materials that can go far above the boiling point of water.

Mirror heating is a non-issue in most direct focus solar furnaces.  They remain cool to the touch while the focal point gets incredibly hot.

[sweitx]

Although key-question.  Does 1400AD tech allows the construction of such massive mirror array for furnace operation?
It would be nice to have mirrors, allow us to direct light from surface to underground...

Just though about an underground temple with just a statue bathed in light.  Or an underground farm lit by mirrors to grow surface food.

If we want to have extensive mirror system, I have a suggestion on how they can be implement.

Mirror should be treated as a construction, made from a bar of silver using metal-smith task.
The mirror need to be constructed outside where the light hits.
You can use the "q" command on mirror to get a cursor that allow you to redirect that beam to a specific location with some limitations (45 degree blindspot below it).  Treat light's path similar to a bolt (will be stopped by obstruction).  Redirecting will be a task and needs a dwarf to set their focal point.
Each mirror will generate heat at the point it's beam hits (increase temperature).
Get enough mirror all pointing to the same spot can make it hot enough to catch on fire, burn noble, or goblin.  Even more mirror will make the tile like a magma (allow furnace operation).
So, what do you guys think?

[LegoLord]

You'd need a massive array of high-quality, modern mirrors to set something on fire.  Cooking could be done.


Basically, no, 1400 AD tech does not allow construction of such a massive mirror array.

[cparax]

I think you're writing off smelting with solar power too quickly. Using platinum and/or HFS, you could achieve a temperature within the range needed to smelt steel without melting the mechanism.

I'd say with some confidence forging that way would be impossible - the setup is too inflexible in shape and optics-dependent to allow for anything but getting something to melt the way you want it - but making steel with platinum/HFS mirrors and crucibles would work fine. It'd logically require limits on what it could smelt - an array using platinum could not smelt platinum or HFS safely, and nothing could safely smelt HFS - but to some degree that's a problem endemic to DF's idea of what can and can't melt and how. In the game as stands, it's perfectly feasible to smelt and forge a metal which would be solid on the surface of the sun in a lead smithy.

[G-Flex]

I think you're writing off smelting with solar power too quickly. Using platinum and/or HFS, you could achieve a temperature within the range needed to smelt steel without melting the mechanism.

I'd say with some confidence forging that way would be impossible - the setup is too inflexible in shape and optics-dependent to allow for anything but getting something to melt the way you want it - but making steel with platinum/HFS mirrors and crucibles would work fine. It'd logically require limits on what it could smelt - an array using platinum could not smelt platinum or HFS safely, and nothing could safely smelt HFS - but to some degree that's a problem endemic to DF's idea of what can and can't melt and how. In the game as stands, it's perfectly feasible to smelt and forge a metal which would be solid on the surface of the sun in a lead smithy.

I think you're confused about some things here.

For one, smelting isn't melting/alloying, and I think you're confusing these terms. To smelt iron from iron ore, you still need a carbon source, for instance.

Also, this sort of solar array heats things up at a focal point. A big vat of iron would probably have trouble maintaining temperature if you're only heating up a very small portion of it, probably.

And your idea that "platinum can't smelt platinum" is kind of silly. A solar furnace made using silver mirrors could definitely melt silver, for instance, because the array itself doesn't get nearly as hot.

And since when is HFS that reflective? You're assuming you can just make mirrors out of any substance.


And the problem with dwarves isn't that they don't have reflective materials. It has to do with the ability and knowledge to build something that huge and that precise with them.

[profit]

this still is not dwarven tech level appropriate... but once again....

THE MIRRORS DO NOT GET HOT!

The ones I have used in focusing the sun to high temperatures DID NOT EVEN GET WARM.

The Focal point gets hot.  The focal point is not even close to the mirrors in most cases.