--- On Tue, 11/2/10, David Scheidt <[email protected]> wrote:
> From: David Scheidt <[email protected]> > Subject: Re: [gurps] A question about Bricks > To: "The GURPSnet mailing list" <[email protected]> > Received: Tuesday, November 2, 2010, 12:32 PM > On Tue, Nov 2, 2010 at 12:46 PM, > Susan Koziel > <[email protected]> > wrote: > > > Not brick making but pottery/glazing... which has some > of the same colour effects (depending on if the bricks are > fired under oxidizing or reducing conditions... the colours > I'm listing are for oxidizing conditions. I am not sure of > reducing condition colours - I do not do enough reduction > firings to know what colours the various oxides give. > > > > Cobat oxide - blue > > Iron oxide - red > > Copper oxide - green > > Manganese oxide - brown > > > > Granted these colours are based on the fact that the > clay body you are using for the bricks is white or grey and > not black or red. > > Red and some of the black clays fire to a red colour > so mixing oxides with them just tends to give muddy versions > of the colour of the oxides. > > > > Different combinations of minerals will give you > different colours due to chemical reactions... so it doesn't > work like a painting where you can mix colours - sure you > can mix the colours but blue (cobalt) and red (iron) do not > give purple... it acutally gives a sort of goldish colour or > a muddy brown - depending on proportions of the mix. > > > > Often time the colour of bricks has to do with the > local clay they made the brick from - typically brick is > made from the cheapest local clay deposit. So the colour is > more a consequence of which of the brick works you get the > brick from. > > > > Only rarely were bricks made of the cheapest clay. > Bricks are pretty > demanding, and using unsuitable clay results in bricks that > fail in > firing, or fall apart, or are not water proof enough. > If you look at > map of historic brick making sites, you can get a pretty > good map of > the geology of suitable clay deposits. You can find > places where > bricks were made of unsuitable materials, because of > difficulty in > transporting proper bricks to the site, or just cheap > bastards doing > the building and not knowing what they were doing. > (the University of > Notre Dame has a bunch of buildings built in the 1860s and > 1870s of > the clay dug from a campus lake. It's not a suitable > material for > making bricks. The buildings require huge amounts of > work to keep > them from falling over. This was pure cheapness on > the part of the > university; perfectly good brick was available to them, > they'd just > have to have spent money on it.) > > > The exception to this is the brick that is made into > high temperature brick - where they take high quality clays > and have specific recipes that allow the brick to survive > high temps or exotic chemical conditions. > > Fire brick is pretty much a uniform yellow/beige > colour > > Modern brick is all made from pretty carefully graded > stuff, even > plain red brick. > Sooo okay - David is correct - I was speaking in terms of a pottery nerd about my experience with brick (I have spent a couple summers playing around with making brick using wood firing/medieval techniques). Which means when I say local and cheap I'm using both terms in a relative fashion... By cheap I mean - porcelin grade clay is the most expensive, work down the line of usable pottery clay for thowing, then get to clay that can't be thrown and was typically used for brick go though that grade of clay, and then get to the kind of clay that can be used for road bases, then get to stuff that is clay but shouldn't be used for making anything. I was not meaning (as David correctly pointed out) that you could just dig any clay out of the ground and use it for brick... rather the clay used for making brick is not as refined as the clay you use for throwing pottery (or you'd slice up your hands). The particle sizes in brick are also less uniform and larger then those you'd use in clay for throwing. (So to me, someone who is basing their cost scale on the clay used to thow pots, the clay for brick is cheap) By local I was meaning - the clay in middle ages brickworks did tend to have distinct colours based on the locale the clay was produced in... by local in this case I meant the nearest suitable clay deposit - not the nearest clay deposit. -Sue (who clearly must remember not to shorten long winded explinations by using relative terms) ;P _______________________________________________ GurpsNet-L mailing list <[email protected]> http://mail.sjgames.com/mailman/listinfo/gurpsnet-l
