Underglaze on top of bisque-fired slip?

[Nell]

Hi,

Would it work to use a decorating slip on greenware , bisque fire it and then decorate with underglazes before clear glazing and firing? I seem to remember someone telling me that the colour of the slip would mix with the underglaze but I don't know if firing in-between would maybe help with that? 

The reason I'd like to do this is for the slip to be the background colour, as I've found it tends to be less patchy than underglaze for larger areas. And for the underglaze to be the design detail on top. 

Is that a sensible way to do it or is there a better way to achieve something like that? I'm fairly new to decorating - any advice appreciated!

Thanks :)

[Babs]

I put slip and underglazes on then bisque. Then glaze and fire.  Less likely to spoil the decoration I have found . I dip glaze, would imagine brushing glaze on would be trickier  if using e the method you are asking about.

You want to test the underglazes reactions to your glaze on vertical tile as some will bleed and run. You need a stable non running clear glaze for starters.

 

[Nell]

Thank Babs.

I'm not worried about the glazing part - when I've dipped bisque decorated with just underglaze it's been fine for the most part.

What I'm not sure about is using decorating slip and underglazes together, and how those colours work together (I should say here that I'm using Duncan Concepts which I'm pretty sure are for bisque only although I know some are suitable for greenware as well). 

Cheers

[neilestrick]

Both slip and underglazes are stiff, so if they don't mix together during application, they won't mix during firing. You can apply commercial underglazes to bone dry, so you could do your slip work at leather hard and let it dry before applying underglazes.

[Nell]

4 minutes ago, neilestrick said:

if they don't mix together during application, they won't mix during firing

Thanks Neil.  That was my concern. That if I had, say, a black slip background and painted a white underglaze pattern on top that it would turn out grey - essentially a mix of the top layer and the bottom layer. 

Out of interest, do you think doing the slip before bisque firing and the underglaze afterwards would make any difference at all to putting them both on leather hard?

Cheers, Nell

[neilestrick]

2 minutes ago, Nell said:

Thanks Neil.  That was my concern. That if I had, say, a black slip background and painted a white underglaze pattern on top that it would turn out grey - essentially a mix of the top layer and the bottom layer. 

Out of interest, do you think doing the slip before bisque firing and the underglaze afterwards would make any difference at all to putting them both on leather hard?

Cheers, Nell

Underglazes aren't entirely opaque, so you may get some of a dark base color showing through a lighter top color. How much it shows through depends on the brand of underglaze and how thickly you apply it.

As for when to apply the underglaze, it depends. For some situations it won't matter if you do it before or after bisque. In other situations it's best to do it before bisque. Some underglazes have a lot of binders and hardeners that make it difficult to get a good glaze layer when dipping glazes. If you bisque fire the underglaze, the binders burn off and it's not a problem. For brushing glazes that shouldn't be a problem. However, sometimes the underglaze can smudge a bit or get picked up by the brushing glaze if it hasn't been bisque fired first. It all depends on which glazes and underglazes you use. Test, test, test....

[liambesaw]

Much to my chagrin, amaco velvet UG white covers not only my dark clay body, but the iron spotting as well.  Had to switch to white slip to get my reduction spotting haha.  Lesson there was to test it out on some stuff you don't care about, and you will know exactly what works, because I feel like it's different depending on who is doing it and how.

[Nell]

15 hours ago, neilestrick said:

Some underglazes have a lot of binders and hardeners that make it difficult to get a good glaze layer when dipping glazes. If you bisque fire the underglaze, the binders burn off and it's not a problem.

Thanks! That's so interesting, you've inspired me to read up on the chemistry - when you understand what's happening it makes much more sense.

And yes, you're all absolutely right - I should do some test tiles.  That's especially good advice considering I usually charge ahead without planning anything!

Cheers everyone. Thanks for your help, much appreciated. 

Nell