search:

Checking The Viscosity of Glaze

Check For Correct Consistency of Clear Glaze

_________________________________________________________________________________

Clear Glaze Viscosity Check

A viscosity cup measures the consistency of glaze or liquid. It is like a ladle and includes a plastic cup or scoop with a single hole on the end of a handle. The hole allows the glaze to flow out. The cup has a handle so that it can be dipped in the glaze.

Simply fill the cup with glaze and time how long it takes for the liquid to dispense through the hole. Our Hobby Colorobbia and Duncan Ceramics Clear Glazes will take about 19-24 seconds to dispense from full to empty.  Note:  not all clear glazes need to be the same consistency - please ask for guidance from your supplier or manufacturer.

Determining The Viscosity Of Glaze

Experience is the best guide to determine the consistency of glaze but unfortunately experience takes a while to develop. A viscosity cup will give added confidence to the novice glazer.

A viscosity cup is a device used to compare or measure the density of liquid. Glaze will usually arrive at “nearly” the recommended consistency. Concentrated or powdered glazes need to be mixed by following the manufacturer’s guidelines or recommendations. However, some glaze containers have no instructions on the labels.

Remember water is the thinnest ingredient in glaze. If there are lots of items to dip glaze or if the glaze itself is stored in a warm environment, then the water will evaporate leaving a thicker consistency of glaze. This evaporation often makes it difficult to calculate whether glaze is too thick - the effects of thickened glaze are only noticeable after an item is fired (and by then it is too late and a piece could get ruined).

Viscosity Cup Guide

(click on the image below to see a video created by Bisque Imports):

You will need a stopwatch or a watch with a second hand.

  1. Please ensure that the liquid glaze is at room temperature (timings can be affected if the liquid is too hot or too cold).
  2. Thoroughly mix the glaze by hand to ensure that:
    a. there are no particles at the bottom of the glaze vessel and
    b. the glaze liquid is in suspension.
    We use a toilet brush to mix our glazes.
  3. Make sure the viscosity cup and mixing appliances are washed thoroughly before and after use. It is advisable to use a cocktail stick each time to clear the hole at the bottom of the cup. This is because dried glaze in the hole can be difficult to see and any blockage (no matter how minor) will distort the timing. 
  4. Submerge and completely fill the viscosity cup.
  5. Lift the cup out of the liquid and record how long it takes for the glaze to flow out of the hole (from full to empty).
  6. Repeat this exercise a couple of times.
  7. Alternatively, fill the cup to the brim while holding a finger over the hole. Start your stopwatch when you remove your finger from the hole. 
  8. The number of seconds is a reliable measure of the viscosity of the glaze. We recommend 19-24.  If the liquid runs through faster, then the glaze is too thin. If the liquid runs through slower i.e. >24 then add a small teacup of water to thin the glaze. Repeat steps 5 or 6 above (and add more water if required) until you are happy with the timings. NB: Do not seek perfection with the timings as they could change each time by the odd second or two.

Click here to find out more about our monthly glazing training course - £50 per person + VAT (or FREE if you buy a kiln from us).

Click here to see more step-by-step guidance from Duncan Ceramics.

Click here to watch a video from Bisque Imports.

Notice

Please note the advice and recommendations given in this document are provided as an aid to novice glazers and firers. The notes given are not step-by-step instructions but are provided as “general” suggestions following years of glazing and firing experience. Country Love Crafts will not be held liable for any sub-standard results as a consequence of the guidelines given. However, please do contact us for advice if the desired results are not achieved.