Western Canada's largest distributor of pottery materials and supplies. Clays, raw materials, tools, wheels, kilns, slabrollers, books & much more.
Our continuing goal is to supply artists, potters and crafts people with great quality products, knowledge and customer service. Our staff is familiar with all the items we stock and can help you through the selection and ordering process. We will also see that your order is shipped according to your directions, or put together for pick up at our retail store in Surrey, BC.
Shipping and Curb-side pick up only
Starting on Dec 1, 2020, this measure is in response to the increase in COVID cases, and is for the safety of our customers and employees. Due to the increasing travel restrictions, and COVID variants, we are monitoring Dr. Henry's broadcasts in order to do our part where possible for our community. We are accepting orders via phone 604-888-3411, and at 'email@example.com'
Help us keep supplies moving smoothly by following these ordering hints:
1. Please allow 2 hours for us to assemble your orders for pick up
2. We kindly request that you consider your order carefully before placing it, so as to avoid making additions. Each addition will add several steps for us, and slows down order assembly
3. If you need to make an addition to your order, we may place you further back in the line, depending upon how busy we are at the time. At worst, this may require treating this as a separate order, so please allow up to 2 hours for us to process any additions
Big thanks to all of our friends, suppliers, and customers!
Thank you so much for your wonderful support. We truly appreciate your patience and patronage, and we all feel so lucky to serve such a wonderful community.
Because COVID case numbers gave us a scare by rising sharply throughout winter in BC, we have seen some increased restrictions. With increasingly contagious variants of COVID popping up, Dr. Henry is advising continued caution in our community as we monitor this new risk. Despite these concerns, there is so much to be proud of our in our continued efforts.
By working together, and by doing little things to keep each other safe, we are speeding up our province's return to normal. I know that it's difficult, that we miss the convenience of our old lives, and that we are all feeling tired of Covid notices, masks, and sanitizer. While we may not have it as bad as our neighbours, we have all still experienced losses in our lives.
Greenbarn's curbside pick-up program is designed to limit personal contact while still allowing us to answer questions, and to safely provide clay materials to our customers. We understand the frustration and inconvenience which is caused by our storefront being closed, but we sincerely appreciate your patience and your willingness to help us to do our part.
With each of us doing that little bit of extra prevention wherever we can, we'll not only halt the rise of cases, and keep the vulnerable safe, but we'll also bend the curve back down. With vaccinations on the horizon, we just need to maintain this trend and work toward enjoying our reward of a 'looser' Spring and Summer!
So, Thank you for doing your part. And, thank you so much for helping us to do our part.
Thank you, and wishing you well, From all of us at Greenbarn.
Technical Tips Blog
Ravenscrag GR6-A glaze with Frit 3134 and Fusion F-12
As this cone 6melt flow test demonstrates, the Fusion F-12 is giving very similar performance to the Ferro. The GR6-A recipe is just 80% Ravenscrag Slip and 20% frit. We confirmed pretty well identical results on clay tiles also. Fusion Ceramics claims that F-12 has the same chemistry of Ferro Frit 3134 and our tests are confirming similar melt behaviour.
Cone 10R dolomite matte effect at cone 6 oxidation
This clay, L4115J3S, a Plainsman 3D-based experimental body, fires vitreous and dense (it contains 0.2% granular manganese). These glazes are very durable and functional. The outside glaze on both is G2934W (adds 10% zircopax). In our C6DHSC firings this produces as matte a surface as is possible without having excessive staining problems. Left mug inside glaze: An 85:15 mix of G2934 matte (without zircopax) and G2926B clear glossy. Right mug inside: G2926B clear glossy ball-milled, over this body it produces a striking visual surface. These mugs look as close to cone 10R dolomite-glazed ware as we have ever seen!
Why do this? We did not have it in stock and customers needed to mix recipes. When the chemistries of the two feldspars are very similar substitution is often not a problem, especially when a recipe only calls for 5 or 10%. However, when a recipe calls for a significant percentage the situation becomes much trickier (in our cone 6 test recipe, "Perfect Clear", 40% Minspar is needed). Feldspars are almost a glaze in themselves, just needing silica and alumina to shift their chemistry toward 'glazedom'. In this project I calculated a mix of materials, in my Insight-live.com account, that sources the same chemistry as Minspar. I made a cone 6 GLFL test comparing the Minspar and Minspar substitute (left) and comparing the Perfect Clear glaze with each feldspar (right). As you can see, the similarity in melt flow is stunning! This is a real demonstration of just how practical and valuable glaze chemistry calculation can be.
Are manganese speckled clay bodies a toxicity hazard?
Before jumping to conclusions consider all the factors that relate. This is M340S, it is fired at cone 6. That temperature is a "sweet spot" for this effect, high enough for the particles to bleed and low enough they do not bloat the body. Such bodies contain only about 0.2% of 60-80 mesh granular manganese (compare this to many glazes that employ 5% powdered manganese as a colorant). Further, the vast majority of the manganese particles are encapsulated within the clay matrix. The tiny percentage exposed at the body surface are under the glaze. It is not the manganese particles themselves that expose at the glaze surface. Rather particle surfaces that contact the underside of the glaze bleed out into it from below, doing so as a function the glaze thickness and melt fluidity. Thus, food contact with a glass surface having isolated manganese-pigmented regions is not at all the same thing as with raw manganese metal. Consider also that the total area of manganese-stained glass on a functional surface is extremely small for this effect.
Serious cracking in a crystalline-glazed P700 Grolleg porcelain. Why?
The cracks appear to have happened on heat-up (because they have widened). Bisque firing was done around cone 04. Issue 1: The cone 10 electric firing was up-ramped at 400F/hr to 2330F (so it whizzed pass quartz inversion on the way!). Issue 2: Wall thickness variations in the pieces, they produce temperature gradients that widen as firing proceeds. Issue 3: Abrupt contour changes and sharp corners, especially when coincident with thickness variations, provide failure points that rapid temperature changes exploit. Issue 4: This new body is more plastic than the previous Grolleg porcelain used, that was likely an enabler to making these thin wall sections even thinner. But remember, practically any piece (unless it has huge in-stresses from uneven drying) can exit a kiln crack-free if firing is done evenly and slowly enough. Results of past firings are the main guide to know what to do in future ones, this is now a "past firing". So the first obvious fix here is slower heat-up, especially around quartz inversion (1000-1100F). Second: more even wall thickness.
By the magic of delflocculation, all this powder will mix into that water
Casting slips require a minimum of water. Amazingly, it is possible to get 3000g of M370 powder into 1100g of water! And the fluid slurry produced, 2250cc, still fits in the container. How is this possible? That water has 11 grams of Darvan 7 deflocculant in it, it causes the clay particles to electrolytically repel each other! An awareness of “the magic” can help give you the determination to master deflocculation, the key enabler of the slip casting process. Determination? Yes, the process is fragile, must must develop the ability to “discover” the right amount of Darvan for your clay mix and water supply. And the ability to recognize what is wrong with a slurry that is not working (too much or little water, too much or little deflocculant).
Two cone 10R bamboo glazes. One stains, one does not. Why?
These mugs are Plainsman H443. The bamboo glaze on the left (A) has 3.5% rutile and 10% zircopax added to the base G2571Adolomite matte. The one on the right (B) has the same addition but in a base having slightly less MgO and slightly more KNaO. B stains badly (as can be seen from the felt marker residue that could not be removed using lacquer thinner). Why does A stain only slightly? It has an additional 4% Gerstley Borate (GB). GB is a powerful flux that develops the glass better, making the surface more silky. The differences in the recipe provide another advantage: (A) has a much lower thermal expansion and is less likely to craze.
These were cast by Anna Lisovskaya, they are fired at cone 03. They are supposed to fit into hexagonal welded frames, but during firing many of them warp enough to fit poorly. Why? The color differences are most obvious here. With that color associates a firing shrinkage difference, the darker ones shrink significantly more. Something less obvious: the sides against the elements receive direct radiant heat, so they shrink more, turning a perfect hexagon into an imperfect one. Terra cotta clays are volatile, that means their approach to maximum density during heat-up, accompanied by shrinkage, happens across a narrow temperature range. Accurate and even firing are paramount. In a radiant-heat electric kiln this can be very difficult. Two approaches could work here: Fire at a lower temperature, perhaps cone 04. Or, greatly slow rate-of-rise for the last 100F, perhaps over several hours.
What is the difference between fahrenheit degrees and degrees fahrenheit?
This is important to understand that when looking at our firing schedule charts. “Degrees Fahrenheit” is a measure of the temperature of something. For example, 212F is the boiling point of water (the equivalent of 100C). "Fahrenheit degrees" are the divisions on the thermometer, there are 170 of them between the freezing and boiling point of water, for example (32-212, while there are 100 celcius degrees for the same span). "Fahrenheit degrees" are thus measures of change-in-temperature, not what the temperature is. In firing schedules, that is what we are talking about, how many degrees should the kiln rise during each step.
Crawling in G2934Y zircon white glaze: There are simple fixes
G2934Y is a fabulous base glaze but it is not without issues. It has significant clay content in the recipe and high levels of Al2O3 in the chemistry, these make it susceptible to crawling. While it is normally fine as is, when you add certain stains to color it (especially at significant percentages) or opacify it using zircon (this has 10%), it can become more susceptible to crawling. On this mug, the glaze layer thickens at the recess of the handle join, that produces crawling during firing. Crawling can also happen on the insides of mugs, where wall and foot meet at a sharp angle. This happens, both because the glaze cracked here during drying and because the zircon stiffens the melt, making it less mobile. Rounding such contours will help. Even better, adjust the glaze recipe so it shrinks a little less on drying (by trading 5% of the raw kaolin for calcined). Adding a little CMC gum (e.g. 0.1-0.2%) will make it adhere better.