One aspect of pottery glaze that people don’t talk about, is silica. Silica is a very key part of pottery glazes though, and adding it to both the glaze and the clay is quite important.
But, does it matter that much in the long run? And how does it affect the state of your pottery?
Well, read on to find out. In this, we’ll discuss the different aspects of silica, and why it matters in your pottery glaze, and why you should know about applying silica to a glaze.
Just What is Silica?
Silica is essentially one of the key parts of both clays and glaze materials.
The purpose of silica is the following:
- It is a glass former
- It creates a glassy nature to your pottery
It is one of the key ingredients in this, and it is pretty much one of the elements that you need to have for any form of glazing.
The materials that contain silica include the following:
- Quartz
- Sandstone
- Sand
- Flint
- Silica Oxide
For many who make their own glazes, they usually rely on the last option for their glazes, since it’s much easier to mix as well.
When you make your own glazes, you need to have silica, but the thing is, you can’t just use silica alone, it needs the other ingredients. That is because silica has the following properties:
- In order for it to melt, it needs to reach a temperature of 3100 degrees
- That is hotter than any kiln can get for the most part
So, if you’re thinking you should just only use silica, you can’t necessarily do that, due to that limitation, so make sure that you know that.
How Silica Affects the Glaze
Silica plays a big part in the way your glazing turns out. For example, it can cause the following to happen:
- Crazing
- Shivering
- The look of the Glaze on the Pottery
Different types of silica change the structures of your pottery, and this is a big thing.
Typically, you should follow the following when applying silica to a glaze:
- Use the 325 mesh as a standard, which is usually listed as flint or quartz silica
- The 200 mesh is alright, but it does affect the glaze firing cycles
- Only use the 200 mesh if you’re working to add this to clay, it doesn’t work as well with glazes
When it comes to using glaze and glaze recipes, you should keep this in mind, and always know that the recipes given are a starting point, and shouldn’t be the only thing that you use.
Why It Isn’t just Silica That Creates Effects
Many people, think it’s only silica, but that isn’t the case. You need to understand why you should use different levels of different elements because it helps with the following:
- It can prevent issues with the glaze
- The right materials will affect the melting temperature
- If you run out of an ingredient, you can substitute it
- This can help you work with glazes better
There is also the unity formula, which is another good one especially if you’re planning on adding silica to your glazes more often than not. The principle behind this is the ratios of different oxides rather than a percentage of the raw materials.
This is good for analyzing glazes, and it involves the following:
- You use the information in order to create a flux of silica and ammonia
- You can then work with this in different ratios
The calculations can be hard and detailed, but if you are able to simplify this and understand the ratios of each of these, you can manipulate the different factors of this. There are tons of glaze calculation programs, and if you plan on getting detailed with the different types of formulas you can use, this is the way to do it.
The Balance Matters
When you’re applying silica to a glaze, you need to make sure that you keep the amount of it balanced up.
If you have too much silica in your glaze, it will create the following:
- A stiff covering
- A white or opaque glass
- An uneven surface on there
- It will be glossy in some ways, but suspended silica can cause crystals to form
- The surface will be harsh and dry
- It inhibits the melting of the glaze
- The glaze won’t be fully on
- It will be textured like sandpaper
All of these are never fun, and you need to make sure that you take the time to best understand why you’re having these issues so that you can better understand the composition
You need to have a balance of this, and usually, it can be due to the following factors:
- Too much feldspar
- Too much alumina in this
- Too much flux
If you want to make a glaze, you want to make sure that you understand each of the parts, and have a good idea of the chemical composition that is necessary for this. If you notice you’re getting overwhelmed with the sheer amount of what you need in order to achieve this, you can always go to the DigitalFire website for a good breakdown of all of the different parts of this.
How to Find Out The Silica in A Glaze Recipe
If you’re looking for where to apply silica to a glaze, but the recipe is a bit confusing, that’s because when you’re trying to figure out where the silica is supposed to be added, it’s usually under the chemical name silica oxide.
That is often under different names too, and you typically want to look for the following words in a recipe, such as the following:
- Silicon dioxide
- Flint
- Quartz
- Pure silica
Look for those when you’re reading recipes, and it will help you with applying silica to the glaze, and how much you need to put in.
Too Much Silica: How Shivering Forms
Yes, there is a chance you might get too much silica in your recipe, and that is how shivering forms. This is one of the most common issues when looking at defects in glaze, and it shows itself in the following:
- Small, jagged pieces
- The pieces detach from the body
- It basically makes the piece unfinished
This is typically seen in functional ware more than anything, and it creates a problem in functional ware because the pieces fall off.
When that happens, the following can occur
- The edges become jagged and sharp, potentially injuring the user
- It can cause this to fall into a food or drink, which is toxic when consumed in many cases
So you don’t want this to happen, that’s for sure, and the best way to rectify this is to look at the silica that you’re including in your body, and apply the following:
- Decrease the amount of silica, particularly in the glaze, but check the body too
- If you notice that there isn’t enough feldspar in the clay, adjust it as needed to create this, since it is an alkaline-bearing material
While this is a common issue in your pottery, if you do notice it happening, don’t use the piece since it can potentially be dangerous, and remake it again with the proper balance of chemicals.
Crazing: When there Isn’t Enough
So, we talked about what happens when it is too much, but what about when there isn’t enough? Well, that’s crazing, and it’s one of the most common defects in glazes, and the easiest to correct.
When you have a piece that crazes, the following happens:
- Small, cracked lines appear in the glaze
- It makes the medium unusable
- It typically can make the pottery piece much weaker, thereby defeating the purpose of glaze
So yes, while crazing may look cool, it’s not the best thing to have to happen to your pottery, especially if you’re looking to use the ware.
Crazing typically relies on a problem in one area, and that is thermal expansion. Basically, the piece expands too much, and then contracts too fast, which is why you get this result when you do use this, and it is pretty easy to correct.
To fix crazing issues, you can do the following:
- Put more silica in
- Check both the glaze and the body, seeing if the crazing is the result of one or the other to fix
- Decrease anything that contains sodium or potassium, and check the balance between the content of the glaze
Now, when you’re doing this, sometimes you may want to purposefully add crazing to the ware. It is a design element, and some people do love that about this, so it may not be something you’ll want to correct.
However, if you do notice it happening more often than you want it to, you should definitely look at the silica balance, and make sure that it isn’t imbalanced.
How to Apply Silica to a Glaze
So how do you apply it? Well, the answer to that is quite simple, and it involves the following steps:
- First, get a recipe for your glaze, whatever you’re looking to make
- Make sure you have a flux, alumina, and silica on hand to create the recipe, whatever it may call for
- Read the recipe, and look at the parts of it
- When you see that it’s in percentage, you’re basically wanting to take that, multiply it by 100 to get the amount in grams
- Get a bucket or media to mix this in
- Mix the ingredients together based on the recipe
- From here, once it’s all thoroughly mixed, you can put it into a bottle, or an application medium
- From there, add it to your clay
- You can fire it, and look at the different results, and if something needs to be changed, you can fix it then
The biggest thing to understand is that you want to make sure that you follow the recipe when you’re doing this. While it may be fun to make your own after a while, when you’re starting out, do make sure you take the time to best understand all of the different facets of this, and really get a feel for these recipes.
Tips for Applying the Silica
Here, we’ll highlight a few of the tips for applying silica to the glaze, and ways to make sure that you get the best glaze possible:
- Always make sure that you follow the recipe
- However, do understand a few of them, such as the ones on DigitalFire, are beginning points, and if you need to adjust as needed, do this
- If you’re using a powder that contains silica, always make sure you have water
- The water should be at least 100mL per 1000 grams of mixing powder
- If the powder you plan to use that contains silica has specific mixing instructions, always make sure that you follow them
- Whenever mixing this type of media period, always make sure you use a respirator and wear gloves, since silica is toxic
- Make sure the ingredients are thoroughly mixed together before you use this on a body
- Don’t use two glazes on top of one another, it causes crawling, another major clay defect
Silica is a key part of pottery glaze, and it’s necessary when you’re applying it to a glaze, which will be used on a body.
Here, you learned all about it, how the right amount of silica matters, and why you need to balance it, so your next step is you can go out, use this, and make the best glaze recipes possible based on the silica levels that you want to have in this body.
