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jbruce

changing specific gravity of glazes

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Hi Y'all,

New to the site. Thanks for having me.

I could not find any software on the interwebs that provides specific gravity adjustments for an existing glaze.  Say your glaze that has been heavily used in the studio has an SG of 145.3, but the manufacturer suggests the SG be 143.  How do I determine how much water I need to add to a bucket of glaze of a given weight to do that? This little form/javascript combination tells you.

https://htmlpreview.github.io/?https://github.com/jbruce12000/glaze-specific-gravity-calculator/blob/master/html/specific-gravity.html

I tested this on a single glaze bucket in our studio and it was right on target.  Can I get someone to verify it for me?

  • use a 100ml graduated cylinder to measure the starting specific gravity
  • set starting specific gravity in the form
  • set target specific gravity
  • weigh your glaze bucket and convert that to grams
  • weigh an empty bucket just like your glaze bucket, they do vary
  • click submit
  • scroll down and find the "new specific gravity" closest to your target
  • add the corresponding amount of water to your bucket (or just to your graduated cylinder if you're nervous)
  • remeasure the specific gravity in the graduated cylinder to verify adjustment was correct

Let me know if it worked.  Also, tell me if there is an easier way.

 

Edited by jbruce

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Welcome.

The online calculator seems to work for its basic function, ie, using water to thin down a glaze, thereby lowering its SG.  

Doesn't work the other way though, ie, separating water out of a glaze to increase its SG, something which is not impossible when you consider that water can often be scooped off the top of a poorly suspended glaze after it has been left standing for a while.  After several tries I can tell you that the target SG must be lower than the starting SG, otherwise the calculator freezes up.  A bit glitchy and probably needs some instructions but otherwise OK.

IMO, in practice, I would not be worrying too much about an SG difference of 2.3 %.  I know that was just an example, but that is really very small. 

Much more important is that the glaze have BOTH an acceptable specific gravity AND viscosity for you to get consistently good application and reliable finished glaze results.   So this is about both flocculation and water content.    This is determined over time as you used the glaze and get the feedback out of the kiln. 

The associated caution is that simply adding endless amounts of water to a glaze is likely to eventually wreck its applications properties.  Rather than worry about a couple of % difference in SG, I would be getting out a zahn or ford cup and looking at viscosity.

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Thanks for the response Curt.

I hadn't thought about going the other direction and removing water.  Interesting... I'll have to ponder whether to include that in this code or make another form to handle it.  Regardless, I'll fix the bug so the form does not lock up and run forever.

I purchased a Ford cup #4, and it'll be delivered this week.  I've read that you should get the specific gravity right before adding flocculants / deflocculants.  Anyhow, how many seconds is ball-park for good viscosity? I've read 15 to 20, but never used a Ford cup, so I have no practical experience.

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OK, didn't know this was your piece of software. 

Suggest you add some general description and overall instructions on top, and some specific instructions to each user input field if they apply: eg, allowable maximums, mins, etc. 

Also the formula for how each column is being calculated.  That would help users understand the result they are getting. 

Also if possible make the column headings stay visible as you scroll down through the page.

the right ford cup number is a matter of preference really, but 15 or 20 seconds is a good starting point. 

I think you are right about specific gravity first, then viscosity but others may have a different view.

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I use a #4 Ford cup, bought from the big river in South America, and I find the correct viscosity for dipping glazes is around 6-7 seconds. S.G. for my dipping glazes is typically between 1.4 and 1.5. Adjust the S.G. first, then flocculate or deflocculate as needed to adjust viscosity. S.G. is a physical adjustment whereas viscosity is a chemical adjustment. Stabilize the physical adjustment first, then make the chemical adjustment.

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This is great!  I made a similar form using google sheets, but it's almost impossible to use on my phone, so hopefully something like this will work (I haven't tried this on my phone yet). Do you mind if I fork your repository to adapt it to my version?

You can find my spreadsheet here: https://docs.google.com/spreadsheets/d/11WFZMq3A6ZtTCneMBRO_5DCOBuNJ3SICMvPkA2YtgB4/edit#gid=0

Actually there are two versions. The second one uses a two-step procedure for when it's impractical to weigh the glaze.

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Curt, I put lots of docs in, fixed the bugs, simplified the table.  I could not find an easy way to freeze headers.

I have not decided about how to handle removing water from the glaze yet.

Thanks for your suggestions.

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