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Would Oil Drops In Compressor Lead To Pin Holes?


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Good morning all,

 

Following in from a previous post where I asked about spraying glaze vs dipping.

 

Just unloaded the kiln and found small pinholes in every piece. Here's the process.

 

Sprayed underglaze

Bisque fired to 1000 Deg C

Approx 20min soak at 1000

 

Bisque sponged and dipped into water, allowed to dry

Dipped glaze (all transparent from same bucket)

Fired to cone 8. Loss of electricity for approx 45 mins at 800 deg with a resulting drop to 500 deg

 

Hubby's theory is that there was a case of oil spitting during the underglaze spraying resulting in small oil drop absorption. If that was the case wouldn't the bisque fire burn off the oil?

 

Would re-fireing help to smooth out the glaze?

 

post-65376-0-59646000-1496208131_thumb.jpg

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From what I can tell from the photo, it looks like your glaze has some thick areas.  If so is the pin holing in the thicker areas of the glaze?  Before you glaze you need to clean your pots so the spitting oil could cause a problem.  Loosing your electricity could also cause pin holing with the glaze cooling down to fast.  Refiring might help, smear a little glaze in the holes and fire your normal schedule for that glaze. Denice

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How are you getting oil into your compressor system? Bad seals? If so repair the compressor or replace. Another option is to use a compressed air tank once to test out the theory.

 

 

best,

Pres

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How are you getting oil into your compressor system? Bad seals? If so repair the compressor or replace. Another option is to use a compressed air tank once to test out the theory.

 

 

best,

Pres

 

Many compressors have an inline water trap. Basically the way they work is the air is passed through oil to remove any water that might be present. This is mostly needed when spraying paints, finishes and lacquers.

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I have found clear glaze especially when used over Underglaze design work needs to be thin or you get pinholes. If the pinholes have any rise to them you will need to hit each one with your dremel to knock it down, then rinse and fill the hole in with a dab of Clear glaze or you risk having a bumpy looking surface once you've re-fired. I have also noticed that pinholes are more likely on the darker blues and blacks. I hope this helps in giving you a few more things to try.

 

T

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Larger compressors can have oil leak past the rings (like in a car engine) as they get used more. Our compressor has a paper filter, right by the compressor plus a water trap closer to the spray gun. Adding an inline filter would take care of it.

 

Re glaze thickness, once you get it to a good thickness I would measure the specific gravity of the glaze then use that as a baseline going forward. Lots of posts here about how to do that if you are not familiar with how to do it.

 

Nice black and tan pattern on your pot  :) 

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I must add to my original post that the pin holes are very small and appear larger in the pic because I enlarged the image

 

why are you not using the sprayer to glaze?

 

The compressor packed up when it came to do the glazing. It had run out of oil!

 

I have found clear glaze especially when used over Underglaze design work needs to be thin or you get pinholes. If the pinholes have any rise to them you will need to hit each one with your dremel to knock it down, then rinse and fill the hole in with a dab of Clear glaze or you risk having a bumpy looking surface once you've re-fired. I have also noticed that pinholes are more likely on the darker blues and blacks. I hope this helps in giving you a few more things to try.

T

 

This clear glaze seemed to be the right thickness. Don't have a hydrometer (will be making one a.s.a.p) so I use the hand method. In this case the pin holes are very small so it wouldn't be practical to fill them and re-fire.

 

Although I think I'll do a re-fire to smooth out the glaze. Thoughts? 

 

Thanks for the feedback, as always it's much appreciated.

 

Andrea

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Hi,

 

I thought I'd let you all know that I re-fired and the pin holes healed. :)  So it loos like the problem was the interruption of electricity during the original fireing.

 

 

As always, many thanks for your input.

 

Regards

 

Andrea

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