(ATM) Ceramic tool quiry & first post

[kferguson@aquilagroup.com]

Howdy folks:
               
As this is first post I will give a short background:

I have decided to take oft given advice and grind smaller mirror before doing 
a "super scope".

I have 8" pyrex blank but no tool. Found much info in archives on tile tools, 
very useful stuff, thanks to all.  Also found tale of "Killian's mirror" most 
encouraging, thanks Alan.

I have looked for unglazed tiles locally , no luck.

I stumbled accross a ceramics store, & thought "Well, what do they make tiles 
out of anyway?" Well, the first store treated me like I must be some kind of 
alien being, but second store was very helpful, so I bought a 25 lb bag of 
clay for $8.  They said thier smallest kiln would handle an 8" disk, and 
firing would cost me $5.  Such a deal! (I could also attend a clayworking 
class Wed. evening for $3....gotta love these people!)

I checked the clay for sand or other grit by dissolving some in water, and 
looking at what fell out of suspension.  It appears to be extremly fine 
stuff, so I'm not worried about scratching during fine grinding.

I made an 8" dia "mud pie". I channeled it like a lap, because Bratislav said 
the spaces between tiles were an advantage.  I have it in my attic drying 4 
days now (it gets hot up there!).  I plan to clean it up with sandpaper 
before firing, as it will be quite easy.

Advantages: Tool is very thick, so I won't wear through tiles.  No cutting of 
tiles to fit round plaster.  No loose tiles, ever. Will take about same time 
to make as tile tool, because plaster needs a week to dry out (according to 
guy at ceramics store) , same as clay.

Now my questions:

1) Will this tool work?  Anyone tried this before? Anything to look out for?

2) I have lost 1/2" to 3/4" diameter due to shrinkage as this tool dried. 
("eyecromiter" measurment).  I assume this is still essentially a "full size" 
tool, right?  Or do I need to make a new mud pie big enough to have 8" after 
shrinkage?  

Sorry if this is old hat topic, I did check archives before posting though.   
                                                                         
Thanks in advance for your exerienced advice.  -KF-