What kind of Ronchi tester are you making Monoxide? I think the easiest way is to print the Ronchi lines on transparent film with a laser printer. But it's not too hard to make a bit better one.
I made my tester according to this idea (the text is in Finnish but there is good pictures):
http://www.teknofokus.fi/Atm/Ronchi/Ronchimake.htm
And here is how it looks like in real life. Nothing fancy, just an aluminium profile, drill, some fishing-line, tape and epoxy. I also mounted a blade to the tester so you can see how the foucault image looks like. The tester is not suitable for actual foucault testing but you don't need that for a 6" mirror.
http://www.allarscopes.com/ronchi_hila/ronchi.htm
There is as many ideas and opinions as there is mirror makers
I made my first mirror (6") simply using two low-expansion glass blanks. I was 16 by then and I didn't have any problems with the grinding. However it was a bit tricky to cast the pitch lap and it took couple of times. I recommend to cast the pitch thick enough. Mine was too thin and I ended up with a turned down edge (the most common error for beginners). However the mirror is not bad at all in overall.
In my opinion you should do your mirror in simplest way. Just two glass blanks and then the pitch on the same conceive blank. There is still lot of glass to grind off in case of some mistake
. You really have to learn this thing and get the right feeling by your own. This is something you can't learn from books.
And finally,
WARNING - YOU MAY GET HOOKED
It happened to me. After 6" I made 12", then 4" and the resent mirror was almost half a meter in diameter
Here is some of my projects (I'm really sorry that it's not in English):
http://www.allarscopes.com/atm.htm
