Would like to tweak a glaze to make it a bit less satin and more glossy

[Bam2015]

I made up 5 gallons of the following recipe, but am now thinking I would like it to be less satin and move towards just a wee bit glossy. I am assuming I should add some silica, but wondering how much? I thought I would measure out three one gallon containers and add a different amount of silica to each, but wondering if anyone can suggest how many grams of silica to add to each gallon container for testing. 

G1214Z
Ferro frit 3124   36
Wollastonite       27
EPK                           35
Silica                           5

                   Total   103 (the poster on Glazy recognizes that this adds up to 103 & states it is not an error)

Here is the link on Glazy.org    https://glazy.org/recipes/1486

 

[Callie Beller Diesel]

The work on that one is likely already done for you. That’s a digitalfire typecode, and here’s a link to Tony’s work on that glaze. It was literally formulated as a demo on how to make a glossy base glaze more matte. 

Don’t get too hung up on the 103 number. The original base glaze likely added up to 100%, but when someone tinkers with a recipe and makes only minor adjustments, sometimes it’s easier to leave the results adding up to an odd number to leave whole numbers for ease of measuring.

https://insight-live.com/insight/share.php?z=7WnpT9vC3b

[Bam2015]

Thank you Callie, but I don't have calcined kaolin or titanium dioxide. I was going by what Sue McLeod recommends for adding gloss to a satin glaze and she recommends silica. I just don't know how much I should add to each one gallon test bucket, so that I can test various degrees of glossy.

[neilestrick]

You don't have to mess with 3 different containers. Take 1 gallon, or whatever smaller amount you want to work with, add 4% silica and dip a tile. Add another 4% and dip a tile. Repeat up to 20% silica added. Personally, I'd use a quart and mix it with a stick blender with each addition. Just math out how much dry material is in that quart based on the size of the original batch, assuming you have precisely 5 gallons. Another way to do it is to weight the bucket of glaze, subtract out the weight of the bucket, then weigh 5% of that into a smaller container. Then take 5% of your original batch size and math out the 4% silica.

[Callie Beller Diesel]

No shade on Sue whatsoever, but Tony is the source of this particular glaze, and you’d be better off looking at his notes in this instance. Here is more related information from the source. https://digitalfire.com/article/g1214z+cone+6+matte+glaze. Long story short, I’d add silica in increments of 2%, up to 10%, just to see what it does.

Titanium dioxide is an opacifier, so it’s only useful if you’re making a white or opaque glaze. It’s an optional ingredient in your case.

Calcined kaolin is made by simply putting some epk in your next bisque, if you don’t want to go to the bother of programming a slightly lower temperature into your kiln just for this purpose. A soup bowl sized container will get you more than enough for this purpose. Usually any time you have a glaze with more than 20% clay, you want to look at calcining some of it, or the shrinking of the glaze slurry on the pot will give you grief.

I’d also suggest starting with 100g samples, rather than an entire gallon of glaze. Unless you’re also dividing the batch out to do colour blends?

[Bam2015]

Thank you Neil and Callie, that's useful info. However, I still don't know how many grams of silica to add to the test glaze whether it's one quart or one gallon. I was hoping that someone could look at the recipe and tell me how many grams of silica they would recommend to add to either the quart or gallon container each time I add silica. I have no idea how many grams to start with. As you can see, I am a real novice when it comes to glaze mixing and trying to learn. 

Edited January 16 by Bam2015

[High Bridge Pottery]

If you know the specific gravity you can work out how much dry glaze you have in the quart or gallon.

 

First you divide the SG of the dry material by itself minus 1. A good estimate is 2.6 so   2.6/1.6 = 1.625

Now you multiply that by the SG of your glaze minus 1. Say your glaze is 1.6 then we would do   1.625 * 0.6 = 0.975

Finally we take 0.975 and divide it by your glazes SG.   0.975 / 1.6 = 0.609375 or 60.9375% dry matter. Then all you need to do is weigh a quart of glaze and multiply it by 0.609375 and you have the total dry weight of the glaze slip and can work out what x% will be in grams.

[Min]

Or you could use Pieter Mostert's Brongniart calculator. You need to know the weight of the glaze materials within the glaze slurry. Brongniart's formula works this out, either longhand or with the calculator.

https://pietermostert.github.io/SG_calc/html/brongniart.html

[Bill Kielb]

5 hours ago, Bam2015 said:

I was hoping that someone could look at the recipe and tell me how many grams of silica they would recommend to add t

This is probably a long shot but - Can you tell us if this was made all in one batch and if so, do you remember the total grams of materials you used. Very often folks making glazes will simply refer to the batch by the material weight, as in, I am making a 5000 gram batch today.

Another idea, I if Sue is illustrating the potential effect of Si:Al in Stull then:

• The original recipe @ 5G silica yields an Si:Al of 5.60:1 (relatively matte in Stull)
• Raise this to 10g and the new si:Al is 6.11:1 ( definitely less matte in Stull)
• Raise the silica to 20g and the new si:Al is 7.13:1 ( under Stull 7:1 is the gloss line)

So maybe mixing 2-3 fresh small 100g test recipes gets you an idea if it is what you like while illustrating how well Stull applies to this recipe. If you find something you like you will have created a target percentage to hit with your mixed glaze.  Then you can go through the calculations mentioned above to figure out how much materials are in your existing liguid glaze and how much silica to add to get to your target. As others have said this recipe has lots of clay so applying this may have challenges. If you like the finished glaze result though you can calcine to make it behave better in application. Maybe simple to make 2-3 very small samples and work from there. It’s always good to start relatively small when testing

Edited January 16 by Bill Kielb

[Bam2015]

Thank you all for your input. I will try some small amounts to test. Thanks Bill.

Betty

[Min]

Agreed it's best to test small amounts before trying to alter an entire 5 gallons of glaze.

Adding silica works up to a point in glossing up a glaze but if the amount of silica needed exceeds the amount of fluxes that are present to dissolve the extra silica then you reach a point where excess silica can't be taken into the melt. Worth a try but might need a plan B if it doesn't, this would be adding more flux along with the extra silica.