I get those on my nabertherm when I put new elements in. I just knock them off with the wooden end of the ZirkonZahn brushes without touching the elements. I do it with a empty chamber. Never had a bad sintering of units even with the bubbles on the elements during the firing cycle. I think it is the nature of this style of element.
This is what I got back from the engineer . It's been a few weeks now and the elements seem to be working beautifully .I will take this as a case of
lol
Hello David,
Please see our engineer's response to the bubbling you are experiencing. Please contact us if you have any questions or need to speak to an engineer.
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Unfortunately, these elements have been severely overheated. The bubbles are Silica, and have been generated by element temperatures in excess of 1625oC.
There are a number of possible causes:
· The insulation may be inadequate, causing the furnace to increase the power to the elements in an effort to maintain the temperature setting of 1530oC.
· The insulation may be adequate, but the thermocouple may be faulty, or sheathed inside the tube in such a way that an inaccurate temperature is being measured, again causing the furnace to increase the power to increase the measured temperature.
· The control equipment may be at fault, perhaps set to power feedback, instead of voltage. If this is the case, full power may have been applied from start-up. This will severely overload the elements. However, I expect once the temperature set point is reached, the furnace should be capable of controlling the power and therefore temperature. The damage may have already been done by this point however.
It will be very useful if the furnace has a chart recording facility, and has saved the data from the first firing. If we can plot the temperature / time data, we will see if the temperature was actually measured correctly. If the temperature remains stable at 1530oC on the chart, it would indicate that the elements have had to work harder to maintain this, for either reason mentioned above. If the temperature is shown to be higher than 1530oC at some points, it would indicate an issue with the control equipment.
I recommend removing the overheated elements and installing a new set into the furnace, once investigations into the cause of this have been carried out. The overheated elements can perhaps be used as part of the investigations, so as to avoid sacrificing another three good elements before solving the problem.
To answer David's question, unfortunately no, this will not go away after a few more firings. The damage has occurred and is irreversible. The elements may continue to operate for an unknown length of time in these conditions, but will most likely fail early.
Please let me know if there are any questions at all.
Best regards,
Michael
( jk ) . It actually gave me a good laugh this morning . Anyway is this normal ? 
