Necessary to Seal Underglazed Surfaces?

[Ben xyz]

I am working with cone 6 Laguna B-Mix (white).
1. I plan first to fire the greenware at 05, then fire the bisque-ware at cone 6.      
2. I will then be applying Amaco Velvet Underglaze color and add underglaze decals, and fire again at 05. I understand often colors will brighten and deepen w/ clear gloss, though my preference is a matte finish. Had tried this firing order and temps before and it worked well (when trying to get a brighter underglaze green). Note: In the future, it would likely be preferable to start out by using a lower fire clay, to reduce the additional firings.

My question now is whether I then have to seal the post-underglazed and underglaze decaled surfaces after this second 05 firing? The ceramic piece will not be used for dinnerware. Will unsealed Underglazes  still be archival color-wise?
I see Amaco has a  lead-free Clear Matte Glaze at c05 (as well as a Satin Clear for c5). Any success with either of these two products? It's stated that their Clear Satin will lighten Velour Black, Jet Black and Light Pink. Another concern is brush-marks; perhaps spraying a clear would be best? Would a matte clear Krylon spray paint be an effective Underglaze sealer? Again, this is a decorative object only, or possibly a vase at most (a gloss would be necessary in the interior of the vessel if that's the case).

 

 

Edited March 25, 2023 by Ben xyz
Clarification

[Min]

+1 for what Rockhopper said.

Couple other points, I've seen 2 brands of commercial underglaze transfers rub off at bisque temps, these in particular needed to go to cone 6 either with or without a covering glaze to be stable. Also, unless you fire the underglaze on the pot the water from applying the underglaze transfer could well disrupt the underglaze layer.

11 hours ago, Ben xyz said:

Will unsealed Underglazes  still be archival color-wise?

Yes as long as they are fired to at least the cone the manufacturer has them rated for.

11 hours ago, Ben xyz said:

(a gloss would be necessary in the interior of the vessel if that's the case)

For cleaning purposes then yes I would liner glaze the pot, however a clay intended to hold liquids shouldn't weep / leak even without any glaze inside. I can't speak to non fired products used to seal the clay. If you only use a ceramic glaze on the inside it needs to fit the clay well or you can get dunting from the tension between the inside and outside surfaces of the clay surfaces.

[Babs]

Personal use ok. If can hold liquid, or food, and for sale you lose control of use so...clear glaze allover imo

Edited March 26, 2023 by Babs
Typos abound

[Ben xyz]

On 3/25/2023 at 7:22 AM, Rockhopper said:

Can't answer your specific question about sealing, as I haven't worked much with underglazes - but I am wondering: 

> If you're not going to apply any glaze or underglaze between firings, why not just fire once to ^6, using a bisque-fire schedule ?

> Why fire to ^6 before applying the underglazes?  Amaco's website indicates the Velvet Underglaze can be fired up-to ^10, and there are ^6 clear glazes available, so it seems like a more traditional (bisque fire > apply glazes > glaze fire) approach would work - and would avoid the challenges that often come with applying glazes to pots that have already been fired to maturity.

The public studio I work out of requests that pieces are bisqued before mid-range firing. Sounds like a straight to mid-range (if nothing is glazed) could save a step. Will take it up with the studio manager. Thanks Rockhopper..

in my experience, the underglaze color shade results can shift considerably between c05 and c5, and even more so at c10. Will do more tests - perhaps some shift more than others. Of course, all can be fired up to 10, but I don't believe the color shade is consistent between low, mid and high firing. Perhaps I lucked out, but did not have a challenge applying the Amaco velvet underglaze to a ceramic surface that had previously reached its fired maturity at c5 and refiring at 05. May not have as much luck with some other colors and different clay bodies.

Since my preference is a matte surface, will also investigate both the c05 matte glaze and even c5 satin, as well as a matte spray sealer. Good to know about the possible issue with an underglaze rubbing off, Min. To avoid underglaze disruption, perhaps best to bisque fire (c05) the underglazed greenware first and applying the underglaze decal after; then re-firing 05. Since I'm not working with utilitarian-purposed objects, handling would be kept to a minimum. Will be trial and error, for sure - appreciate the responses! 

 

Edited March 27, 2023 by Ben xyz
Clarification

[Ben xyz]

Questions I posed to Amaco concerning their velvet underglazes. Will post their response.

[Ben xyz]

Sorry about this snapshot format. I tried a copy and paste, but since I work on a black background for emails, the type here came in as white on white. The font size was also quite large. Their prompt response was appreciated:

[Kelly in AK]

Nice to see the professional/commercial interests have a similar response to what you hear here: Test it first, see if you’re happy with it. “You could fire the velvet underglaze onto a vitrified clay surface. However…” I’m constantly amazed at what commercial products pull off. Big engineering energy. If you’re not doing functional work, then if it looks good it is good.

Sculptural work does not suffer the same beatings as functional pots, nor are room temperature finishes forbidden. On the other hand, nothing will last like properly glazed ceramic. 
 

 

[High Bridge Pottery]

15 hours ago, Ben xyz said:

I tried a copy and paste, but since I work on a black background for emails, the type here came in as white on white.

Not sure if this option is on phones but on my desktop if you right-click you have "paste" and "paste as plain text". The plain text option will remove all the colour and size formatting and get you back to the normal forum font style and colour.

[Ben xyz]

Thanks High Bridge - likely a workaround with the cellphone as well. 

Will need to wing it and hope for the best as far as unglazed underglazes go, in terms of archival lightfastness (since my preference is a matte surface). The other option is sealing the underglazes with their matte c05 clear (or satin c5), and doing tests to check for color shifting and number of coats needed.  Trying to avoid cloudy/lightened colors. Have heard about one glaze out of Australia that seals the work but does not visually alter the surface (though pricey). Surprised there aren't more options out there for those of us who prefer matte surfaces on occasion while working w/ underglazes. The other option is using paints, as done by artist Ken Price. Thanks for input, Kelly.

[Roberta12]

2 hours ago, Ben xyz said:

Thanks High Bridge - likely a workaround with the cellphone as well. 

Will need to wing it and hope for the best as far as unglazed underglazes go, in terms of archival lightfastness (since my preference is a matte surface). The other option is sealing the underglazes with their matte c05 clear (or satin c5), and doing tests to check for color shifting and number of coats needed.  Trying to avoid cloudy/lightened colors. Have heard about one glaze out of Australia that seals the work but does not visually alter the surface (though pricey). Surprised there aren't more options out there for those of us who prefer matte surfaces on occasion while working w/ underglazes. The other option is using paints, as done by artist Ken Price. Thanks for input, Kelly.

Have you explored Terra Sigillata?  Gives a great matte, soft, color of your choice, surface.

[Ben xyz]

2 hours ago, Roberta12 said:

Have you explored Terra Sigillata?  Gives a great matte, soft, color of your choice, surface.

I have not, but will be learning more about the process in Glaze Application classes next month. I'm guessing that Mason stains can be incorporated into Terra Sigillata? Looking forward to obtaining fuchsia and other brighter colors.

[Callie Beller Diesel]

Mason stains can be incorporated, but with caveats.

Stain particles are larger than ball clay ones, so you have to add stain to Sig after it’s been siphoned.  If you add stain before, most of it winds up in the discard sludge. Be aware you will likely have to mix frequently during application to keep everything evenly suspended. But it does give nice results. 

Also, if you use any sig methods involving ball milling, that can alter several stain colours. It isn’t recommended for encapsulated ones at all.

 

[Ben xyz]

3 hours ago, Callie Beller Diesel said:

Mason stains can be incorporated, but with caveats.

Stain particles are larger than ball clay ones, so you have to add stain to Sig after it’s been siphoned.  If you add stain before, most of it winds up in the discard sludge. Be aware you will likely have to mix frequently during application to keep everything evenly suspended. But it does give nice results. 

Also, if you use any sig methods involving ball milling, that can alter several stain colours. It isn’t recommended for encapsulated ones at all.

 

          Had considered this method, after having bought pre-colored porcelain once ($$$). Good info to have for the future - thanks. If I understand correctly, this would involve using stains with slip, correct? Wondering if Mason stains are colorfast? With all that heat and light from firing, my guess is that they would be. Will check on their site to be sure.
        Still find it odd that Amaco sells their "Velvet Underglaze" line when they can't vouch for its unsealed surface (kind of negates the flat 'velvet' aspect and description).

[Babs]

41 minutes ago, Ben xyz said:

          Had considered this method, after having bought pre-colored porcelain once ($$$). Good info to have for the future - thanks. If I understand correctly, this would involve using stains with slip, correct? Wondering if Mason stains are colorfast? With all that heat and light from firing, my guess is that they would be. Will check on their site to be sure.
        Still find it odd that Amaco sells their "Velvet Underglaze" line when they can't vouch for its unsealed surface (kind of negates the flat 'velvet' aspect and description).

Underglaze is made for just that! Useit any other way and Company won't vouch for it.

[Callie Beller Diesel]

22 hours ago, Ben xyz said:

If I understand correctly, this would involve using stains with slip, correct?

Think of using stains the same way you do iron oxide or other colourants. Ceramic stains are pigments that let us get colours that are difficult to achieve, or may offer a much safer way to use oxides like vanadium or cadmium. They’re designed to have low reactivity, which is why they can look kind of flat if a glaze is oversaturated with them, or if it’s used as a sole colourant. They can’t be called completely non-reactive because some are affected by some things while in the kiln, but they’re not affected by things like daylight or air.

They can go in slip, terra sig, clay bodies, glazes, all the things. They do tend to be more expensive than just a raw oxide might be because they’re engineered. Using them in large quantities in, say a casting slip, is still going to be kinda spendy, but if they’re 1-5% of a recipe they’re an affordable way of introducing colour to low and mid fire work. Making that coloured casting slip yourself is generally less expensive than purchasing one someone else made.

Re colourfastness and ceramics: you’re right about things that survive kilns being fine on the colour front. Fading isn’t really a concern. There’s a couple of specific exceptions to that rule ( copper raku glazes, a glaze that fails a lemon test), but of all the things people worry about in a glaze, colourfastness is probably at the very, very bottom of the list.

[Jeff Longtin]

Back in the 90"s I was commissioned to make 200 porcelain figurines. I found a sculptor to sculpt the piece and then I made 10 production molds. After showing the customer a cast piece, unfired, they asked me if I could paint the piece. As I knew they couldn't finish the piece I agreed to include that in the project. (It was for a group home for people with severe disabilities.)

Never having worked with "Amaco Underglazes" before I went out and bought about 20. Almost all of them were disappointing. (Except Medium Blue and Bright Yellow.) Frustrated I decided to "make my own".  I bought a pint of the Amaco LUG white Underglaze and a bunch of Mason Stains.

I experimented with mixing them, in various amounts, and found the homemade version to be quite good. There was a lot of frustration, but after awhile, I found a group of colors that safely went to cone 6 and were mostly opaque. 

[PeterH]

On 4/10/2023 at 10:27 PM, Ben xyz said:

Had considered this method, after having bought pre-colored porcelain once ($$$).

2 hours ago, Callie Beller Diesel said:

Using them in large quantities in, say a casting slip, is still going to be kinda spendy,

... although in this case you could reduce the cost by casting a thin coloured layer backed by a thicker white one. (But might have issues where the white shows.)

e.g. https://ceramicartsnetwork.org/daily/article/Slip-Casting-Ceramics-Using-Colored-Casting-Slip
Wet the mold with a sponge. Pour the colored casting slip into the mold and let it set up for approximately ten minutes (figure 5). Then pour the colored slip out of the mold and let it drain  figure 6). Once the slip has stopped dripping from the mold, immediately pour in the white casting slip. Leave the white slip in the mold for about 30 minutes before draining. The longer you leave the slip in the mold the thicker the piece will be. I prefer to make my pots just a little on the thicker side.
 

[Min]

9 hours ago, PeterH said:

... although in this case you could reduce the cost by casting a thin coloured layer backed by a thicker white one. (But might have issues where the white shows.)

+1

this is what I did for tumblers

 

[Ben xyz]

Nice tumblers, Min. Thanks for casting technique, PeterH. Was thinking I'd start with a zinc-free matte (and/or satin) clear glaze, and adding  stains to those, do tests, and see what holds up at c05 and c5 on white clay bodies. Since I was looking for fairly concentrated (flat) colors, my thoughts had been that adding stains to a flat white may result in a semi pastel, but sounds like that may not be the case, from your results Jeff. The stain addition to a slip makes sense too, Callie. I understand that an excess of 10% stain to any base won't change the color anymore. Time to invest in several stains. I believe Mason stains are better for some colors and US Pigments for others.

[Callie Beller Diesel]

It sounds counterintuitive, but add a bit of zircopax to glazes. It’ll pop the stain colours a bit. 1-3% will do.

 

[neilestrick]

On 3/30/2023 at 5:10 PM, Ben xyz said:

Surprised there aren't more options out there for those of us who prefer matte surfaces on occasion while working w/ underglazes.

The nature of glazes is that opacity increases as they become more matte. There's a limit to how matte a surface can be a still remain transparent.