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Old 2019-01-09, 3:27pm
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Speedslug Speedslug is offline
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Join Date: Mar 21, 2009
Location: Winnebago, MN
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Three other ideas come to my mind ....

The first is batch dependent from the manufacturer ... the size of the tumblers they use to mix the raw ingredients together can be pretty big particularly if it is a very popular glass ... so the amount of the various chemicals added to the basic glass recipe can be from ounces to pounds.

As a result the mix will vary somewhat and when you finally get your hands on it a temperature change of 15 degrees f one way or the other could easily change the way your current batch will strike in the kiln.

That is the one that I would be putting my money on if I were a betting person.

The next is the one that Kathy mentioned; Temperature probes are made of two kinds of metal that produce a voltge change when heated and if you are using them a lot one would expect them to change a little bit over time ... again it only takes 10 or 20 degrees one way or the other.

Yet another possibility is the control system that the temperature probe feeds into. This is less likely to be the source of this change but it is possible.
A little bit of corrosion on a wire from the probe can change the signal it puts out, a small bug that got through the screen could have died in a wrong place and changed the signal going into a control chip changing the heating signal but not the displayed signal.

Then there are the relays or SCRs (silicone controlled rectifiers) feeding power to the heating elements that handle a LOT of power / current / heat and some changes with age should be expected with them as well.

When we are using temps of 940 degrees a change of 10 degrees is only a little over 1%.

As a technician type myself, I am surprised that we don't hear of over striking more often.

As for the batch mix ratios I think that colors like Coral having such wide variations is a really good example of just how sensitive the ingredient quantity and quality can be when trying to get one particular color out of a glass melt from one month to the next over decades.
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Last edited by Speedslug; 2019-01-09 at 3:31pm.
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