Hydrophobic surface for spouts

[kswan]

I've been trying to understand the physics of a dribble free spout (on a pitcher or teapot) for quite some time now and I'm curious to know if other people have information to share on this. I have read some scientific articles that talk about things over my head, like hydrodynamic suction and flow rates. I haven't even made a teapot in years because at least half of my pitchers' spouts dribble when I test them, and I end up with a collection of things I can't sell. I have tried many variations on angle of the spout, having a thin lip, curving the edge of the lip inward to help cut the flow, wiping away the glaze from the lip, etc. Every time I meet a small pitcher like for soy sauce or cream at a restaurant, I examine it closely if it works properly. Metal ones almost always work perfectly, even if they are all sorts of different shapes. At my house, I look at the coffee pot, the electric kettle, Pyrex measuring cups, my Yixing teapot, and anything else I can try to see if there is some magic formula to make mine work perfectly every time. Why does metal work so well? Like those discs you put in a wine bottle to stop it dripping. 

I feel pretty certain that my clay body and glaze are working against me. I have made some well-functioning spouts in the past with a different clay body in a class and had not a drip in sight. The clay had sand in it and was meant more for handbuilding, but for some reason it made a perfect spout with little effort on my part. I had heard from another potter that a swipe of butter under the lip can stop drips. Every time I try that, no matter how good or awful the shape of my spout, the drips completely stop! But who wants to sell a piece and say to a customer, "Just put butter on it every time you use it"?  

I'm looking for a material (clay, slip, glaze) that I can make or apply to a spout for a pitcher or teapot that will behave as hydrophobic to get my spouts under control. This winter I'm going to try teapots again and I'm going to try to copy the design of my Yixing spout. I use B Mix 5 clay without grog.  The Yixing teapot isn't glazed, and when I leave glaze off the end of my spout, it still doesn't create enough of a cutoff. I don't want to have to fuss with how fast you pour it, or what angle. I just want it to work! 

Any ideas on a water repellant surface other than butter?? 

[Min]

42 minutes ago, kswan said:

Any ideas on a water repellant surface other than butter?? 

A very very thin almost not there swipe of clear silicone works too. But you can feel it if you touch it so for me that's a no go too.

[PeterH]

Two trivial points.

They sell water-repellent treatments for windscreens. I don't expect they are food safe, but they might give you an idea how useful a really water repellent surface would be on an experimental spout.

Not too certain about this, but epoxy may have a lowish surface tension.  IIRC people have mentioned food-safe epoxy in other postings.
Typical values of surface energy for materials and adhesives
https://www.twi-global.com/technical-knowledge/faqs/faq-what-are-the-typical-values-of-surface-energy-for-materials-and-adhesives

May be true
Food Safe Epoxy – Helpful Guide about Food Grade Epoxy
https://resin-expert.com/en/guide/food-safe-epoxy

PS I expect that the matt surfaces of super-hydrophobic substances would get clogged over time (BTW I live in a very hard-water area). 
How to Prevent Teapots from Dripping
https://news.softpedia.com/news/How-to-Prevent-Teapots-from-Dripping-125869.shtml

 

[Hulk]

Good question

Perhaps super glossy glaze, polished, then waxed?

It is possible to make drip free spouts that don't depend on applying hydrophobic film to the drip area; as noted, they are examples that prove. 
I'm still looking for the practical definitive authority on dripless spouts.

Meanwhile, here's where I am with it*:

To me, it says when the liquid is flowing fast enough to "detach" from that lower edge, there's no dribbling; when the flow rate isn't fast enough to cause detachment, there is dribble.
Hence, design such that
  a) the flow rate required for detachment is lower,
  b) and the transitions between no flow and high flow (and high to none) are very quick.

Seems to me there's still work to be done to share the findings in everyday terms for practical application, heh.

*from this thread: https://community.ceramicartsdaily.org/topic/30337-teapot-pour

 

 

[kswan]

@Hulk I had just reread that post of yours, and good work with the teapot! It looks like your clay has some grog in it, am I right? It seems like that may play a part in helping prevent drips.

@Min @PeterH I'm thinking of something to be fired on, rather than applied after firing. I wonder if a very stony matte glaze would work, just at the cut edge of the lip. Or brush on a slip that's rougher textured and leave it unglazed, but my Yixing teapot is a very smooth clay body, so that can't be the only thing. 

Is there a way to find out water's hydrophobic reaction to clay/glaze materials, or is that something to just test out on my own?  I seem to recall something about this in the back of my brain somewhere, that you can check this on fired glazes by putting a drop of water on it and seeing how much it spreads out or forms a ball. My clay and glaze let it flow too much, and I wonder if there is a known specific material (ie sodium flux versus calcium, kaolin versus ball clay) that helps with this.  Does sand or grog have an inherent ability to cut the flow? 

[Bill Kielb]

5 hours ago, kswan said:

Why does metal work so well? Like those discs you put in a wine bottle to stop it dripping. 

Ever try making the leading edge as sharp and smooth as practical and recruiting gravity to help. The rounded nature of glass seems to influence things quite a bit and the smooth rather sharp finish of metal seems to help remove the troublesome dribbles for many liquids. We have always tried to use smooth flow (laminar), gravity and a well finished leading edge to help with the dribbles. This has seemed to work well over the years for us https://youtu.be/BAwo5cKhCuM

 

Edited November 17, 2022 by Bill Kielb

[PeterH]

2 hours ago, kswan said:

Is there a way to find out water's hydrophobic reaction to clay/glaze materials, or is that something to just test out on my own?  I seem to recall something about this in the back of my brain somewhere, that you can check this on fired glazes by putting a drop of water on it and seeing how much it spreads out or forms a ball.

Are you thinking about measuring the contact angle? My knowledge of the subject ends with its name, but here are a couple of google hits:

Contact Angle: A Guide to Theory and Measurement
https://www.ossila.com/pages/contact-angle-theory-measurement
... which a least has some helpful pictures

Simple Contact Angle Measurement using a Smartphone (Easy Guide)
https://www.youtube.com/watch?v=s3DrTJk3CFA
... which  tries to offer a half-way house between judging things by eye and the use of specialised equipment

 

[Babs]

Might have to work on your pouring action too, or place a finger over hole in lid to give a what do you call it effect...:-)

Brings to memory a very old friend who dallied between cups without altering the angle of the pot, chatting sweetly away. That pot dripped!

[kswan]

Yes, @PeterH, that is what I was thinking of. I didn't know what it was called, but I'd do it the low-tech way visually!  

@Bill Kielb Thanks for sharing your video. I've tried all kinds of sharp. Sharp on the inside. Sharp on the outside. Razor thin lip (which works but leads to breakage). Angled up. Angled down. Wide spout. Narrow spout. Agh! I haven't tried sanding the bisque surface of the spout, but it still probably wouldn't make that much difference given my track record! 

I'm going to experiment with this, especially on the glaze side of it. It just seems logical to me that I should be able to make a glaze (or bare clay body) that can behave the way that butter does.  I'd love to be able to just get a spout done without endless fussing and disappointment. Sigh.

[Min]

Looks like nanoparticle titanium dioxide is being used in self cleaning or hydrophobic glazes for washroom sinks and toilets. From this article, there are quite a few more articles if you search for nanoparticle titanium dioxide in hydrophobic ceramics. 

[kswan]

This could be a fascinating avenue! Thanks, Min! 

[Chilly]

On 11/17/2022 at 4:12 PM, kswan said:

Metal ones almost always work perfectly

worst dribblers I ever saw were stainless milk jugs and tea and coffee pots in British Home Stores cafes.