Gothic Arches

Everyone has likely seen beautiful carved stone arches in the Gothic or Medieval style. If you wanted to build a castle, you probably wouldn't mind having some of these included in your design. I'm sure you're capable of carving these yourself out of stone.... What's that? You're not a stonemason? Ok, just hire guy to spend a few hundred hours carving individual arches.... What now? You can't afford that? OK, here's my idea, cheaper and DIY:

First of all, building an arch for a window yourself does not alleviate your responsibility of making sure that it is structurally sound and meets all code requirements, and if you actually try to build one using my ideas and you get hurt, it's not my fault! These are just ideas!

After watching too many DIY shows and now the Mythbusters (they make all kinds of cool stuff in their pursuit of destruction...er, science, I mean) it seems the best way to make a nice decorative arch for a window would be to form one out of cement by using a mold of RTV or some similar material.

Now, there's no getting around the fact that you are going to have to make an arch, at least one yourself, that is exactly what you want. I'll have to leave the construction method up to you, but several ideas come to mind. Pour plaster into a cylinder or approximate shape of the arch segment you are constructing and carve it to the appropriate shape (time consuming and difficult to maintain the accuracy of alignment when done in segments). You could block together an arch out of craft or large foam blocks and carve that to the desired shape (easier and cheaper). You could also build the whole thing out of wood (not too easy, not too cheap, but very durable). Either way, you'll have to build it at least once, taking into account the structure it will sit in, appropriate room for supporting and installing glass and affixing the whole thing to the structure of the building.

Once you've built the window frame, (I'll assume wood for the sake of not writing three different versions), you'll want to make sure that it is precisely the trueness, shape and quality you want for your finished product. You'll be using it as mold. Every imperfection or error will come out in the end product.

Build a wooden form capable of surrounding your arch laid flat, the form must have two halves. Make sure it is strong enough to support cement and will not "blow out" due to the weight of the material. You'll need to look for a mold-making how-to online at this point, I could fill a couple of pages on how to make a mold like this; if I find one, I'll post it. EDIT: Here's a video You can scale it up and use more appropriate mold making materials to make it larger. Once your mold is made and you extract your original part, you'll be able to pour as many cement molds of your arch as you want. You could even lay re-enforcing bar or wire mesh inside the mold to have strong, reinforced cement in the end possibly capable of bearing structural loads. One could make large windows and incorporate a hollow frame to hide or place a structural support inside. You could create door frames, gargoyles, decorative wall caps, decorative heraldry, all out of cement; durable, beautiful, and limited only by your imagination and what you are willing to try.
I have noticed that some of the mold-making materials are somewhat pricey, but when you consider what it would cost to make these things out or real stone, the price is considerably more reasonable. I suppose if you were good at it, you could sell some of your creations and make some money on the whole thing!

Another how-to here.

The "mouth" or "face" arch picture is part of T. E. Breitenbach's Castle.