Antique Greenware

[Juli]

I recently acquired A LOT of greenware pieces that were thrown in the 70’s and 80’s by a local artist.  Yes, greenware!! I need to fire it but the gentleman does not remember what type of clay he used back then . Any suggestions on what cone I should try????  I know it is not low fire. 
If I fire a high fire clay to cone 4 or 5 what happens? My max for my kiln is Cone 8. So if I fire mid range and glaze with a mid range glaze and it is a high fire clay what happens. 
I am a newbie and I have never fired my kiln but I have it installed and ready to go. My son who has autism received a pottery wheel for 16th birthday so I have to learn.

I have really tried to find an answer to this question but to no avail. 

[LeeU]

What kinds of forms are these?  More info is useful---basic size/weight/shape and what will they be used for? Functional or sculptural?   I've been stuck using high fire clay with commercial mid fire glazes & firing to ^5-6, and it all worked out just fine (not vitrified to maturity tho) but these were non-functional pieces and were not going to be subjected to water, heat, or weather. Some photos would help.

 

[oldlady]

why do you want to fire these pieces?

[Benzine]

At the very least, you could strengthen them a bit, by putting them in a bisque fire, which is going to be about the same regardless of the type of clay. 

Fire them to Cone 04 or 05, which will make them a whole lot stronger than they are as greenware.

After that, you could "sacrifice" one, and begin firing it at increasingly higher temps.  Start at Cone 5 or 6 and go from there.  I should note, that if your kiln is rated for Cone 8, that is the hottest it will get with brand new elements, and only a couple times after that.  From that point on, it will only get to Cone 5 or 6. 

Before you bisque fire the wares, I would also buy some clay, that rated for whatever the highest temp you plan on firing them to.  Make some rimmed dishes or plates  to go under the wares.  Bisque fire those along with the old pottery.  Have them sitting on the dishes/ plates you made, when you start firing them hotter.  This will protect your kiln and kiln shelves in the event that the old pottery melts. (This answers your question of what will happen to the pottery, if you over fire it.  Low fire clay will melt at mid and high fire temps, and mid fire clay will melt at high fire temps.  How much they melt is dependent on how over fired they are.  I bought a damaged second hand kiln that likely had low fire clay, fired on the high end of mid fire ranges.  The projects melted into nearly unrecognizable mass, and started to eat into the bricks on the kiln floor. 

If you under fire the clay (say it's actually a high fire clay and you only take it to mid fire temps) it just won't be functional  The clay won't be fully vitrified, and would absorb and seep liquids, on any bare spot. 

So a lot of things to consider, it kind of depends on what your end goal is with them, and whether or not you are OK with losing one of them in testing.