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Thread: Coffee cup coating
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21st February 2019, 10:58 AM #1Woodturner with a shed
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Coffee cup coating
Ok, that looks like a nice deep, controversial rabbit hole to dive down into...
I want to turn a coffee cup, not a travel mug but a cup. I don't want to use an insert or the like. So I need a coating/ finish.
Low maintenance
Heat resistant (good, hot, black coffee temp)
No nut oils (just to be on the safe side)
Any suggestions?
Thanks
Redbeard
Cheers
Redbeard
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21st February 2019 10:58 AM # ADSGoogle Adsense Advertisement
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21st February 2019, 11:18 AM #2.
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I'd start with some Clay.
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21st February 2019, 11:50 AM #3Woodturner with a shed
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21st February 2019, 12:07 PM #4GOLD MEMBER
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Raises many complex questions Redbeard. Very complex & difficult question (ie a deep rabbit hole)
Heat resistance short term to say 90 C? Would wood like that? Getting wet? getting hot? Without cracking?Non tainting / no taste / non toxic?
Its a difficult ask. Letting my imagination soar… “brainstorming” it was called… these options come to mind:
1. Speciality food wax blends (incl high purity synthetic waxes) as used on some paper / cardboard cups etc throwaway kinds (many are proprietary) may be available from food film manufacturers but they are interested in high volume sales only. Ask for test samples
2. Metal films : compliant think soft stickable , buthow to stick them to wood surface (gold foil is stuck to wood, wont stain but it lacks any abrassion resistance- would look fantastic! ) and seal them? which metal .. Gold? Silver? Aluminium all possibilities. Stick / Glue Alfoil to the inside? Maybe!
One could coat the inside with graphite and electroplate a metal to the inside (eg black nickel) if one protected the outside from plating chemicals. It can be done with plastics as well as organic & plant materials
3. Polymers: but which? Polyethylene (low melting but how to apply) polypropylene good as melts higher temps but adhesion? They are good food plastics but cant be bonded to wood easily .. BUT f you used them as a liner and wood as a holder it would work, but that's what you want to avoid
4. Others: 2 part (eg epoxy .. health issues) acrylic (same) cyano acrylates (maybe as they cure with water)
5. Oils: many air hardening oils available and many that stay soft but waterproofing taste / tainting problems exist
I think making a HOLDER for a liner (paper plastic / metal / ceramic) you can live with is best. But you could explore 1 & 2 further
Euge
Last edited by Euge; 21st February 2019 at 12:12 PM. Reason: typos
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21st February 2019, 12:11 PM #5GOLD MEMBER
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Add to the flavour - use wood from a coffee tree.
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21st February 2019, 12:16 PM #6Woodturner with a shed
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21st February 2019, 12:17 PM #7Woodturner with a shed
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21st February 2019, 12:19 PM #8Woodturner with a shed
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Euge
Thanks for the brainstorm ("they" call it a brain- DUMP these days, sounds messy to me).
Food for thought.
Cheers
Redbeard
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21st February 2019, 01:08 PM #9GOLD MEMBER
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Maybe the boss (Neil) could suggest if any of his wood coatings are suitable for hot food / beverage contact?
Why not PM him Redbeard? He would have an informed professional view on wood coatings
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21st February 2019, 01:11 PM #10.
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I wasn't being flipant.
Wood has practically zero of lasting at those temperatures and the 100% humidity without a lining.
It is possible to do one or the other but not both.
There's no known wood coating that can handle those sort of conditions for too long.
And well before it dies and within short order it will look extremely ordinary.
A type of coffee cup that would last a bit longer than others would be a small chunky espresso cup.
Ristretto (15mL) shot made in ~20s and knocked back in one go Italian style within a minute of being made.
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21st February 2019, 01:47 PM #11Woodturner with a shed
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Certainly, without a lining wood will most likely fail in the proposed use hence me looking for a coating or lining. If necessary I would use some form of full encapsulation to seal the wood (thinking epoxy or similar).
I have built fresh water tanks on boats with epoxy coated plywood and these are still around 20 years later. If I can keep the moisture out surely less than 100 degrees is not going to hurt the wood. The wooden spoons in my kitchen are still going strong after many years of in and out of boiling pots without the wood failing.
I like a Ristretto as much as the next caffeine junkie but I prefer to linger over a larger cup of the black stuff.
Cheers
Redbeard
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21st February 2019, 02:03 PM #12Woodturner with a shed
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Looking back on that last post I realise I contradict myself. The wooden spoons haven't failed and with a bit off a scrub and some oil they look quite respectable still. The same with my wooden chopping boards which go through the dishwasher on occasion.
Based on that, 70-100 degrees is probably not enough to make wood fail, it's probably lack of maintenance which causes it to fail. I don't want to have to maintain the wood of my cup so I need to isolate it from the world around it. Hence a coating.
There are industrial paints capable of resisting much higher temperatures, used in much more aggressive environments so I was wondering if there was something available for my more pedestrian application. Preferably clear(ish) and definitely cheap (because I am).
I think that last bit may cause a problem.
Cheers
Redbeard
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21st February 2019, 02:46 PM #13.
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Industrial pants work on low uniform expansion materials like steel.
The problem with Wood is it typically expands and shrink about 1/4 that of steel parallel to the grain and 3x that of steel perp to the grain.
This differential expansion will eventually crack any rigid coating like epoxy.
If you have to use a flexible plastic coating you might as well use a liner.
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21st February 2019, 02:48 PM #14GOLD MEMBER
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I recall an IWCS friend and noted turner in Sth Aust (Nev S., now deceased, lived Gawler way) was an excellent turner of goblets and had an excellent collection of them.. Like me, he then used Rustin's 2 part finishes for his goblets and they looked fantastic. Just a point - the wood of the bowl portion was very thin 2-3 mm which may give it more flexibility with temp changes. Maybe some were used for red wine, I don't know.
I believe there are now more good coating options and many would pass the the temperature test, but do they pass a taste (tainting) test?
Euge
edit: there are two causes of expansion in wood, thermal and moisture induced changes . Which can be avoided? Not the former with these coffee cups.
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21st February 2019, 03:50 PM #15Intermediate Member
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I made the wife a Blackwood Kuksa for her birthday last October and finished the outside with Tung oil. She seasoned the inside with strong black coffee and vodka for a few days and it has come up a treat after 5 months of use.
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