Jump to content
Sign in to follow this  
fayechristian

Gold Lustre and Alkaline Glaze

Recommended Posts

I have just started experimenting with Gold and Platinum Lustre in liquid form. I have found it difficult to find much written about the topic and I wondered it anyone could give me some advice.

 

I remember from college that it should not be used on over an alkaline glaze but I do not know how to identify an alkaline glaze. I would also like to know why it shouldn't be used on an alkaline glaze.

 

I work with a limited pallet of 4 stoneware glazes, a copper green, a copper blue, an iron brown and a chrome pink.

 

I have experienced a few different issues, one of which is a dulling of the glaze on the whole pot, the copper green goes much darker after a lustre firing and the Iron brown turns nearly black while the copper blue and chrome pink do not change at all.

 

The other issue is I get a very matt gold surface on both of my copper glazes, neither of which I would call matt glazes. But a high shine on the iron glaze and chrome pink.

 

Would love any words of wisdom

Share this post


Link to post
Share on other sites
Guest JBaymore

Lusters are covered quite well in "China Paint and Overglaze" by Paul Lewing.

 

best,

 

...............john

Share this post


Link to post
Share on other sites

I have just started experimenting with Gold and Platinum Lustre in liquid form. I have found it difficult to find much written about the topic and I wondered it anyone could give me some advice.

 

I remember from college that it should not be used on over an alkaline glaze but I do not know how to identify an alkaline glaze. I would also like to know why it shouldn't be used on an alkaline glaze.

 

I work with a limited pallet of 4 stoneware glazes, a copper green, a copper blue, an iron brown and a chrome pink.

 

I have experienced a few different issues, one of which is a dulling of the glaze on the whole pot, the copper green goes much darker after a lustre firing and the Iron brown turns nearly black while the copper blue and chrome pink do not change at all.

 

The other issue is I get a very matt gold surface on both of my copper glazes, neither of which I would call matt glazes. But a high shine on the iron glaze and chrome pink.

 

Would love any words of wisdom

 

 

Hello Faye

Welcome to the world of Overglaze and lustre. It is a world of myth and misconception.

 

 

I work extensively with lustre and up to this point have never come across any reference to not using resinate lustres over alkaline glazes. However there may be some confusion happening here as Arabian lustre (also known as clay paste and reduced lustre) certainly requires an alkaline glaze for the sub strata. Alkaline glazes are those containing alkaline fluxes. Googling alkaline fluxes will give you a whole list. You can identify alkaline glazes through looking at their composition. However most glazes have some percentage of alkaline flux in their composition. I guess it is the percentage of the type of flux that gives it its label. However highly alkaline glazes can and do change some colours from oxides, the most notable one being copper. It can change from green to blue in an oxidising atmosphere. So I suspect that your copper blue glaze is an alkaline glaze. Without knowing the composition of your copper green glaze I wouldn't be able to tell.

 

From my observations you may be encountering two separate issues here. One deals with lustre and the other with refiring a glazed work. This being said what temperature are your stoneware glazes fired to and what temperature are you firing the lustre to?

 

1. Lustre is a thin film of metal deposited on the surface of a fired glaze.

 

  • It is NOT a glaze in itself. It relies on the glaze interaction with the lustre for adherence and this can be anywhere between 720.C-820.C depending on the hardness of the glaze. Earthenware glazes are usually refired between 720-750.C while stoneware and porcelain usually refire between 780-820.C but that is not set in stone. Every glaze is different and you would have to test to find the common denominator for your glazes. Glass, depending on the type, starts to accept lustre from 600.c onwards. You will know if you haven't fired high enough as the lustre will rub off. If fired too high it will start to burn off and be patchy. Commercial porcelain blanks can be tricky to find the optimum temperature as a lot of these follow the procedure of high fired bisque with a low fired glaze. This appears to be the same with bone china.
  • It takes on the characteristics of the glaze it is on. If the the glaze is very glossy then the metallic layer is very glossy. If the glaze is matt then the metal layer is matt and this then follows on for all the permutations in between.
  • However I have noticed in my own work that copper glazes seem to be more problematic as my lustres always seem duller. This then brings me to the second point.

 

2. Certain glazes when refired at lower temperatures change their appearance and characteristics to some degree.

 

  • It seems to common knowledge that high iron glazes change their properties when refired from approx 900. - 1000.C?? and held at a particular temperature for a specific time. It allows microscopic crystals to grow and give a different colour and texture to the glaze. This has been exploited quite liberally. I have a feeling that some Shino glazes also fall into this category. At lustre temperatures there does not seem to be a change in the texture/gloss of tenmoku glazes and I have no experience of iron brown turning nearly black. My oxidised tenmokus are nearly black before I lustre them.
  • In my experience copper glazes also seem to undergo change when refired but at a lower temperature around 800.c. I am not a chemist but I suspect that it has something to do with the copper reacting as you may be aware that copper glazes fired in oxidation can be refired in a reducing atmosphere around 800.C to give copper red which sits on the surface of the glaze rather than in the glaze matrix. Seeing as resinate lustres carry their own reducing medium on board whilst being fired in oxidation I feel that there might be enough reduction going on to change the glaze characteristics as well as the lustre characteristics.

 

I may be shot down in flames for this last statement but these are my own observations after having tested many permutations of putting lustre on copper glazes at the temperature I fire to which is 810.C Gold, copper and platinum lustres seem to duller and the glaze itself is different.

 

One of the best texts that I have found on lustres is "Lustres for China Painters and Potters" by Heather Tailor. It is definitely out of print but can be picked up second hand through Amazon and other second hand book sellers as well as through Ebay occasionally.

 

Johanna

Share this post


Link to post
Share on other sites

Thank you all! I've never used the forum before but it's been amazing to get responses. I will head straight off to the library to try and find the books you have suggested.

 

Thank you Johanna for taking the time to reply to my post in such depth, what a great answer. It's brilliant to get a response from someone who clearly knows a lot about the subject. I've just ordered a copy of the book you suggested from amazon, thank you. It's also really reasuring to know that what I've found is well documented and it's not something I'm doing wrong, its just a lack of knowledge, which I can improve on.

 

I fire to 1260.c for a normal stoneware firing and as I couldn't find much written about lustre the first time I used it, I cobbled together what I could and punted for 800.c lustre firing with a 10 minute soak to even the final temperature. I have always had good adherence of the lustre to the glazed surface except for the odd blob where I presume it was too thick and burned away. I might try 780.c and no soak to see if it reduces the change in the glaze colour of the glaze.

 

I really appreciate all of you help!

 

Faye

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Sign in to follow this  

×
×
  • Create New...

Important Information

By using this site, you agree to our Terms of Use.