Bubbles in glaze help!

[weberceramics]

Hello!

I make customs platters using all low fire products. I have been using the same materials for about a year now. Recently after my glaze fire (cone 06) my platters have been coming out with bubbles/pinning.  I saw a method in another post saying to sand and reglaze. So I did…. They came out with them again. Can anyone help me? 
 

thank you in advance 🙏🏼

Edited November 25 by weberceramics

[Hulk]

Nice detail with the cobalt.

Is there bare clay showing?
These are the defects? ...the window one, looks like bare clay.

My guess would be there's something(s) in the clay that is/are "off-gassing" to make pinholes, however, those markings seem very big, pencil size.
If so, a) more thorough bisque fire - not necessarily hotter, but more time (and oxygen) to burn out impurities, and
            b) drop and hold glaze fire to allow the glaze to "heal over" the marks, and
            c) apply the glaze to a reasonable thickness, but not too thick!

Had the troubles begun with a new batch/bag of clay?

[weberceramics]

10 minutes ago, Hulk said:

Nice detail with the cobalt.

Is there bare clay showing?
These are the defects? ...the window one, looks like bare clay.

My guess would be there's something(s) in the clay that is/are "off-gassing" to make pinholes, however, those markings seem very big, pencil size.
If so, a) more thorough bisque fire - not necessarily hotter, but more time (and oxygen) to burn out impurities, and
            b) drop and hold glaze fire to allow the glaze to "heal over" the marks, and
            c) apply the glaze to a reasonable thickness, but not too thick!

Had the troubles begun with a new batch/bag of clay?

Thank you!

Yes, the arrows point to a bubble form and pinholes and when I sand it there is no glaze under. Yes, this is a new bag of clay. However, when I create other items with the same clay but different glazes - it doesn't happen. Should I sand down the bubbles and add an overall coat of clear glaze or apply it only to the sanded parts? I have never done a drop-and-hold. Is that just putting a number for the hold? What time should I put in for the hold? I have a MAS1823HE Olympic Kiln in my home studio and have never done that!

Sorry for so many questions!

[Roberta12]

@weberceramics  I have had a similar problem with a specific clay (a mid fire porcelain) My remedy was to sand down the spot and put clear on just that spot and refire.  It always worked.   It would be something to try.  I called the clay company and did not get a clear answer from them.  And this happened with different clear glazes.  Not any other glaze.  Just the clear.  My solution was to switch clay bodies.  But I did do the spot refiring lots of times at cone 5/6.  

Roberta

[Hulk]

Filling just the spots might be better, as Roberta suggests.

Here's an article on drop & hold:
Drop-and-Soak Firing

How thick are you applying the glaze (first time)?

The large circle marks - haven't seen those before, interesting.

The defect in the window, looks like the glaze layer is quite thick.
How thick is it?

Edited November 27 by Hulk
curious, how thick?