Iridescent/Mother-of-Pearl Finish

[Ben xyz]

I'm looking for a glaze that would create a clear iridescent (oil slick/pearly) finish and can be applied over most other glazes. Saw one from Mayco and another from Amaco. Duncan's product was also recommended. Preference? I understand it would be very low fired, similar to a temperature used for metallic lusters. Thanks!

Edited February 24, 2023 by Ben xyz
Clarification

[Callie Beller Diesel]

Mother of pearl is a lustre and fires to cone 016, but that’s from memory, so double check the label for specifics. Ibelieve the Amaco and Mayco ones are both pretty similar. 

Definitely use a vapour respirator and apply outdoors! The stuff is pretty stinky, and very not good for you. 

You want to apply it evenly and not too heavily, or it will go hazy instead of pretty. Use brushstrokes that go against each other in a hashtag motion, or in a swirling pattern. If you apply it all in the same direction, the iridescence doesn’t show as well, or only from one angle. 

[Ben xyz]

Interesting info about the application - thanks Callie. Will be trying both Amaco and Mayco's lustre and report back. Will also be applying outdoors as suggested. Also will look into a vapor respirator. Wondering if the iridescent effect degrades at all over time? Archival issues are paramount when it comes to painting, but haven't seen the term mentioned much in regards to ceramics and glazing (maybe I'm not looking in the right places). Recently learning  here (on another post) that magnesium will degrade over time in Palladium glaze was eye-opening, and has me questioning the permanence of other glazes and colors. 

Edited February 25, 2023 by Ben xyz
Clarification

[Callie Beller Diesel]

In regards specifically to MOP, my husband has a unicorn statue from his mom that she made back in the 70’s that’s all done in MOP and gold lustre. It shows no surface degradation after 45 years of sitting on a shelf. She’s the one who gave me the application tips when I was playing with it. (Thanks Marilyn!)

Archival discussions around pottery and ceramics are definitely different than in painting! Firing clay has prehistoric origins in function, and it’s the bulk of how ceramic is used as a material, so durability thresholds start at very different points. No one would dream of subjecting a painting to the abuse ceramic items take. We’re always talking about making things that hold up to freeze/thaw cycles,  acid attack, thermal shock and cutlery marking. Half the discussions on this forum are some version of “if I do ___ will that break something and if so, how?”

That said, there are a few categories of glazes that can and do react with oxygen if left unsealed, but they’re outliers and there’s all kinds of warnings and caveats about their suitable uses. Not everything we make is utilitarian after all, so there’s some room for these things. Think raku fired wares involving copper, and some glazes that are over saturated with some heavy metals, like Palladium having a lot of manganese. (Not magnesium. That’s different, but it’s easy to confuse.)  

Modern lustres are their own weird thing. They’re not technically a ceramic finish, and they’re not used exclusively on pots. They aren’t bonded with the glaze, or other substrates they're applied to. It’s just a really fine layer of metals sitting  on the surface of something shiny.  They’re made from metals that don’t oxidize, such as yellow or white gold, but they are subject to mechanical and some chemical degradation. That’s why you usually only see lustres on the rims of china pieces where they get less wear, and you’re not supposed to put grandma’s china in the dishwasher. They don’t recommend you put mother of pearl on food surfaces, because it can wear off. You can sand lustres off with elbow grease and some 220 grit wet/dry sandpaper.