How to Mix Pottery Glaze

Intro to Mixing Dry Glazes

Mixing a glaze powder with water allows you to apply the glaze to bisque ware quickly and easily.  It is a relatively simple process.  The main steps, in more detail below, include: measuring water, mixing the glaze powder with the water, sieving, adjusting viscosity or density and letting the glaze sit for a while before it is applied.  There are many variations and some people execute these steps in a different order.

First of all, follow the instructions that came with the glaze if you are using a premixed powder.  Many commercially prepared glazes can now be purchased as dry powder in 10, 25, or 50lb increments.  Generally, dry glaze powder is formulated for dipping and pouring, while premixed liquid glazes are formulated for brushing (3,20).  The following instructions assume that you have a glaze in dry powder form which is mixed well and ready to be mixed with water.  If you are not using a whole batch of premixed powder make sure it is mixed well before taking part of the powder to mix with water.  Some of the glaze ingredients might settle to the bottom of the container during transport (20).  There are also many suggestions for keeping the glaze suspended in water or improving brushability.  These suggestions include Flocs (7), bentonite (3,11), epsom salt (13), brushing medium (10), CMC (11) and Macaloid (13).

Glaze Mixing Safety

Glazes are most dangerous in powder form because they can create dust which can be inhaled very easily. Some glazes also contain toxic chemicals.  Always wear a NIOSH certified respirator or mask and mix the dry powder outside or in a well ventilated area.  Many people also recommend using rubber or latex gloves while working with a glaze (7).  Don’t put your fingers near your eyes,nose or mouth while working with the glaze (16).  You can also use safety goggles to make sure glaze doesn’t get in your eyes (20).
Also: don’t eat the glaze powder!

Materials and Equipment

glaze mixing materials and equipment

1. Clean buckets and lids
2. Water (proper amount for your glaze)
3. Glaze powder
4. Hand held drill
5. Jiffy/Hanson/Turbo/Drywall Mixer or paddle
6. Sieve (with proper mesh for your glaze)
7. Respirator
8. Dust Mask
9. Safety Goggles
10. Rubber/Latex Gloves
11. Paint Brush
12. Spatula, Rib, or other tool
13. Hydrometer or Viscosity/Zahn Cup
14. Rags/Sponges

Glaze Mixing Instructions

Every glaze is different and everyone seems to have their own way to mix them.  This is a basic outline but feel free to try things your own way or change the order of the steps.

Measure out Some Water

Measure water into a clean container with a volume at least 25% (20) more than your final glaze volume.  Great Clay recommends using a 3-4 gallon bucket for 10 lbs. of powder (7).  If you bought a premixed glaze it will probably tell you how much water to use.  It’s easier to add more water later if the glaze isn’t thick enough so it is recommended that you start with 90% of the total water required (20).    Every glaze is different so the amount of water will probably be different as well:

Many people recommend 11 fl. oz. of water for every 1lb. of glaze powder (3,10,20) or 8 oz. for spraying, or 7 oz. for brushing (3).

Great clay recommends 1/2 pint of water for every 1lb. of glaze powder (7).

Laguna suggests:
dipping – 10.5-11.5 oz water, 0-2.3g bentonite, to 1lb dry glaze
spraying – 7.5-8.5 oz water, 1.1-3.4g bentonite to 1lb dry glaze
brushing – 6.5-7.5 oz water, 4.5-6.8g bentonite, 2.3-3.4g CMC powder to 1 lb dry glaze.
(11)

Some typical examples for spectrum dry glazes include:
10lbs. of cone 06/04 clear gloss glaze – 6.25 pints of water
10lbs. of cone 4/6 opaque gloss glaze – 5.25 pints of water
10lbs. of cone 4/6 clear gloss glaze – 5.25 pints of water
10lbs. of cone 4/6 Reactive Hi-Fire glaze – 5 pints of water
(1)

Glaze mixer states that most glazes are about 50% water so for every 1000g of powder you would add 1000mL of water (5).

Add Glaze Powder to the Water

There are a couple ways to do this.
It’s ideal to add the glaze powder to the water instead of water to the glaze powder but you can add a little water at a time to the powder until you get the right consistency (7).

You can dump the powder into the water without stirring and then mix when all the powder has become wet (6).

You can also pour or sift/screen/sieve the powder in gradually as the water is mixed or agitated (5,10,11).

Mix the Glaze Powder and Water

The glaze needs to be mixed really well to prevent problems when applying the glaze to bisque ware.  You can begin mixing your glaze with a stick (8), toilet brush (22), whisk (12) or something similar but Spectrum doesn’t recommend manual mixing (20).  Attachments such as a drywall mixer (4), Jiffy/Hanson mixer (7), Turbo Mixer (10), or just a simple paddle (20) can be attached to a hand held drill to mix the glaze.  (Don’t drop the drill in the bucket!)  You can also use a kitchen blender to mix smaller batches, just don’t use the blender to make any more smoothies after mixing the glaze (12).

Put the Glaze Through a Sieve

The glaze will most likely have small lumps of glaze that aren’t mixed completely with the water.  Putting the glaze through a sieve will eliminate these lumps.  Sieves come in different mesh sizes.  The number represents the number of openings per linear inch in the screen (19) so the higher the number, the more fine the screen (4).  Using an 80 mesh sieve seems to be the most common suggestion but check your instructions since suggestions range from 50 mesh (6) to 100 mesh or finer (4,10,13).  Some glaze instructions might specifically tell you NOT to sieve the glaze (10).

If you don’t have a Talisman Sieve or something similar, you can push the glaze through the sieve with a rib (3), brush (22), spatula (15), or your hand with a rubber glove (4).

Sieve the glaze at least once (4), or twice (5,22) or even three times (2,6).  Just make sure there are no lumps left in the glaze.

Check Density and Viscosity

The glaze needs to be the right density and thicknesss because if it is too thick or thin it can cause problems when it is applied to the bisque or when it is fired (20).  Many people use a well known liquid as a comparison to get the glaze to the right thickness.  For example, a glaze might need to be about the same consistency as cream or heavy milk (7), whole milk, heavy cream, half and half, etc.  You can use a viscosity cup or “Zahn cup” to measure the thickness or viscosity (20,22).

You can also check the density or “specific gravity” of your glaze with a hydrometer if you have one.    For checking glazes a hydrometer that measures specific gravity in the 1.000-2.000 range seems to be the best option.

Temperature is also a variable in measuring specific gravity (9) and most hydrometers will tell what temperature they are calibrated for.  It is easy to get a false reading on a hydrometer (12) and some say that hydrometers aren’t reliable, especially with a suspension like a glaze (14) so you can also measure a certain volume of the glaze, weigh it, and then divide that number by the weight of the same amount of water to find the specific gravity (9).  Specific Gravity, after all,  is just the weight of the liquid divided by the weight of the same volume of water (20).

Every glaze is different and might require a unique density.  The application technique you decide to use can also help you decide the density of your glaze.  For example, Laguna recommends the following for their glazes:

color dipping: whole milk — 1.611 (55 Baume)
clear dipping: half and half — 1.465-1.48 (46-47 Baume)
spraying: heavy cream  —-  1.706 (60 Baume)
brushing: slightly thicker than cream  — 1.813 (65 Baume)
(10)

Spectrum recommends dipping glazes have a specific gravity between 1.50 and 1.70 and brushing glazes in the range of 1.45 to 1.60 (20).

Check with the company that makes your glaze if you are using a premixed glaze.  For example, Standard Ceramic Supply provides a standard gravity for individual glazes.

You can also use the knuckle test to see if your glaze is about the right consistency.  If you dip a clean, dry finger in the glaze it should cover your finger but you should be able to see the lines in your knuckle (4,8) or the glaze should cover the skin but bead on the fingernail (18).

Glaze mixer suggests a glaze consistency similar to cream but also recommends applying the glaze to a bisque pot and then chipping some of the glaze off to confirm that the glaze is the proper thickness (5).

Once you have tested your glaze and found the right density you can weigh a certain amount of the glaze and then make sure the same volume of future batches have the same weight (12).  This will help you get more consistent results.

Adjust the Density or Viscosity

If the glaze is too thick/dense you just have to add water, a little bit at a time, until you get the proper density/viscosity.  It takes less water than you think to change the density (6,9).

If the glaze is too thin you can let the glaze sit overnight and then scoop or skim off some of the clear water that rises to the top (17) or add more dry powder (9) if you have some left.

Let Stand for 24 Hours

Once you mix your glaze you should let it sit for a while before you use it.  This allows all the particles in the powder a chance to soak up the proper amount of water.  You can do a final check on the viscosity and or density to make sure the glaze didn’t thicken too much overnight.  Or some people just wait to check the density/thickness until they are ready to use it.

Mix and Apply to Bisqueware

Stir or mix the glaze before you apply it to the bisque ware and do it consistently throughout the application process.  Some glazes have heavy particles that can settle out quickly (20).  It is especially important to monitor the density or thickness of a dipping glaze because the bisque pieces can suck up extra water as they are dipped (20).

Store the glaze in an air tight container and make sure it is clearly labeled (5).  Also make note of the glaze density or thickness after you have tested it so you can get consistent results the next time you mix a glaze.

If you mix glazes a different way or have any additional tips leave a comment below.

Other Resources

Standard Ceramic Supply: water suggestions, Specific Gravity
Hydrometer Conversion Table
Online Conversions
Material Safety Data Sheets
3M Mask/Respirator Selection Guide

References

1. http://www.baileypottery.com/glazes/spectruminstructions.htm
2. http://www.bigceramicstore.com/information/makingglaze.htm
3. http://www.bigceramicstore.com/information/MixingGlazes.htm
4. http://www.ehow.com/videos-on_2771_make-clay-pottery-glazes.html
5. http://www.glazemixer.com/howtomixaglaze.htm
6. http://www.goshen.edu/art/DeptPgs/glazMIX.html
7. http://www.greatclay.com/Merchant2/merchant.mvc?Screen=CTGY&Category_Code=DGMI
8. http://jennygulchpottery.wordpress.com/2008/09/28/glazing-pottery/
9. http://jessehull.com/2008/01/26/specific-gravity/
10. http://www.lagunaclay.com/glazes/dry-glaze-mixing.php
11. http://www.lagunaclay.com/support/dry-glaze-mixing.php
12. http://www.lakesidepottery.com/HTML%20Text/Tips/Mixing%20and%20Using%20Glazes.htm
13. http://www.nmclay.com/Customer_service/DRYGLAZEMIXING.htm
14. http://www.potters.org/subject45630.htm
15. http://www.potters.org/subject76701.htm
16. http://pottery.about.com/od/applyingglazes/tp/beforeglaz.htm
17. http://www.pottery-magic.com/pottery/glazes/recipes/mix_glaze.htm
18. http://shop.clay-planet.com/usingglazes.aspx
19. http://www.sigmaaldrich.com/chemistry/stockroom-reagents/learning-center/technical-library/particle-size-conversion.html
20. http://www.spectrumglazes.com/tips.html
21. http://www.standardceramic.com/glazehandout2.pdf
22. http://www.youtube.com/watch?v=RLIGelEX9VY