Follow Slashdot blog updates by subscribing to our blog RSS feed

 



Forgot your password?
typodupeerror
×
Technology

Engineering the Perfect Coffee Mug 145

Nerval's Lobster writes "From the annals of Really Important Science comes word that a research assistant who picked up his B.S. just seven months ago has invented a coffee mug designed to keep java at just the right piping-hot temperature for hours. Logan Maxwell, who got his undergraduate degree in chemical engineering from North Carolina State University in May, created the "Temperfect" mug as part of his senior design project for the College of Engineering. Most insulated mugs have two walls separated by a soft vacuum that insulates the temperature of a liquid inside from the temperature of the air outside. Maxwell's design has a third layer of insulation in a third wall wrapped around the inner basin of the mug. Inside is a chemical insulator that is solid at room temperature but melts into a liquid at 140 degrees Fahrenheit. The insulator – which Maxwell won't identify but swears is non-toxic – turns to liquid as it absorbs the extra heat of coffee poured into the mug at temperatures higher than 140 F, cooling it to a drinkable temperature quickly. As the heat of the coffee escapes, the insulating material releases heat through the inner wall of the mug to keep it hot as long as possible; a graph mapping the performance of a prototype shows it could keep a cup of coffee at between 128 F and 145 F for as long as 90 minutes. "Phase-change" coffee-mug insulation was patented during the 1960s, but has never been marketed because they are difficult and expensive to manufacture compared to simpler forms of insulation. While working on the Temperfect design, Maxwell met Belgian-born industrial designer Dean Verhoeven, president of consulting form Ancona Research, Inc., who had been working on a similar design and had already worked out how to manufacture a three-walled insulated mug cost effectively. The two co-founded a company called Joevo to manufacture the mugs." According to the Joevo Kickstarter page, you can get one starting at $40. For that much, I'd like a clever lid like this Contigo has.
This discussion has been archived. No new comments can be posted.

Engineering the Perfect Coffee Mug

Comments Filter:
  • by stevel ( 64802 ) * on Thursday December 12, 2013 @06:18PM (#45675109) Homepage

    This is just the same approach as Coffee Joulies [joulies.com], which is a former Kickstarter project. I have a bunch of these, they work well. No need for a custom mug.

    • This is just the same approach as Coffee Joulies [joulies.com], which is a former Kickstarter project. I have a bunch of these, they work well. No need for a custom mug.

      Well, it's not quite the same as coffee joulies, for a number of reasons.

      First, it's integrated/built in.
      Second, well ... you won't lose the integrated joulies.
      Third... uh ... different name.

      Seriously though, this is just an improvement on the thermos. A fancy improvement, and it might even be more effective ... but it's not breaking new ground.

      • Re: (Score:3, Insightful)

        by vux984 ( 928602 )

        Seriously though, this is just an improvement on the thermos. A fancy improvement, and it might even be more effective ... but it's not breaking new ground.

        Nothing that hits the shelves as a consumer product is ever 'breaking new ground'. Its always standing on the shoulders of what came before; and has already cut its teeth in niche markets that needed and could afford the high early adopter price for research and development for the incremental improvement over what was already out there.

        • Two layers of insulation? Push, I have three layers!

        • by donaldm ( 919619 )
          One of the points of the article is how people like their coffee at 140 deg F (60 deg C). I would love to know how he arrived at the stats for that since people who like drinking coffee like it at varying temperatures, from "iced" coffee to hot which can be over 80 deg C (which I prefer by the way). It really depends on the drinkers preference. To me 60 deg C is insipid, still that is a personal opinion.

          To me the very idea of paying US$40 for a cup that will keep coffee at an "insipid" temperature is not
          • Based on my (admittedly non-scientific) testing, between 140F and 150F is the sweet spot where the coffee flavor is the most intense while still being reasonably hot. Hotter than 150, I don't taste the flavors of the coffee as much. Cooler than 140, it doesn't feel like a hot cup of coffee. YMMV...
      • by icebike ( 68054 )

        Plus the joulies clunk around in any mug, making a fair bit of noise.
        Use them in an open topped mug and they smack you in the teeth as the mug gets emptier.
        And they displace beverage, meaning you need a refill sooner.

    • by ackthpt ( 218170 ) on Thursday December 12, 2013 @06:33PM (#45675257) Homepage Journal

      This is just the same approach as Coffee Joulies [joulies.com], which is a former Kickstarter project. I have a bunch of these, they work well. No need for a custom mug.

      Sometimes the reason for having is in the having, not in the utility. Any geek knows this.

      If Apple sold an insulated iMug people would queue up for it. You know this to be true.

      they'd also be suing samsung for patent infringement with their damnable galaxy adro-mug

      • Can I get mine with a peltier cooler and USB^H^H^HLightning port?
        • You're already getting phase change. How greedy are you?

          I'll take mine with some of these pallets generating too much heat at Fukushima.
          Not hot enough for industrial power production? Ship it here, I would save some gas.

      • They'd also patent rounded and bevelled coffee mugs.
    • Re: (Score:2, Informative)

      It's actually not. All the Joulies do is act like a thermal mass that takes "excess" heat from the coffee to heat them up (cooling the coffee) and then just make the cooldown process slower due to the extra heat capacity provided by the Joulies.

      As noted in the summary and on the Kickstarter page, these mugs use a phase change material to absorb the extra heat and basically play it back as the coffee would otherwise cool.

      Another very common phase change material is ice and the behavior is very similar
      • by jcochran ( 309950 ) on Thursday December 12, 2013 @07:05PM (#45675505)

        Sorry, but it's EXACTLY the same approach. As others have mentioned, this mug works like coffee joulies does. And interestingly enough, the paraffin wax that coffee joulies uses melts at 140 degrees Fahrenheit. I would be extremely surprised if Logan Maxwell wasn't also using paraffin. It's cheap, readily available, and non-toxic. The only thing different is the extra layer of insulation around the cup.

        • by inicom ( 81356 )

          Came to say this - the description sounds exactly like they are using a layer of wax.

        • Hmmm.... take a look at this coffee mug [amazon.com]:

          The two layers of porcelain, which are separated by a hollow cavity, act as a perfect insulator for hot and cold beverages and ensure that you wonâ(TM)t burn your fingers. A silicone stopper in the cupâ(TM)s base prevents water from entering the hollow cavity when washing the mug.

          So, take out the plug, fill with melted wax, replace plug, and enjoy?

        • "wax" was the first thing that popped into my head when I read " The insulator – which Maxwell won't identify but swears is non-toxic". Not a whole lot of cheep, non toxic materials with that particular melting point out there.
        • Analysis at http://www.crcweb.org/Sappirim/Sappirim%2023%20(Mar%202012).pdf [crcweb.org] suggests the wax is “is most likely palmitic acid which has a melting point of 61–64C (142–147F) or possibly myristic acid (which has a melting point of 49–58C / 120–136F)”.
        • by drkim ( 1559875 )

          It could also be sodium acetate.

          • That was my first guess too, but I was looking to see if someone else had the same idea.

            Checking Wikipedia, "Sodium acetate trihydrate crystals melt at 137.12ÂF / 58.4ÂC, (to 136.4ÂF / 58ÂC)"

            ... which I think leaves sodium acetate in the frame too.

            • by drkim ( 1559875 )

              ... which I think leaves sodium acetate in the frame too.

              That was my first thought when I heard the description. Especially when they mentioned the solid -> liquid transition.

              • Especially when they mentioned the solid -> liquid transition.

                Same applies to the paraffins too, though IIRC they've a lower specific heat of fusion.

                I recall my Dad having a wrenched wrist muscle which he had to heat treat several times a day by building up a "wax cast" onto it. Probably the waxes used there were around the right temperature range too.

                With the waxes you could adjust the useful temperature range by mixing two waxes.

      • by stevel ( 64802 ) *

        Yep - as jcochran says,it's just a repackaging in a dedicated mug. The Joulies web site says:

        "Their polished stainless steel shells are full of a very special phase change material (an ingredient in food) that melts at 140F. When you put them in your coffee this PCM begins melting, absorbing a LOT of heat in the process and cooling your coffee down much faster than normal.

        "Where does all that heat go? It’s stored right inside your Coffee Joulies. When your coffee reaches 140F (the perfect drinking tem

    • Unless you've got incredibly hot coffee under pressure not really the same thing as this phase change material :)
      It's just adding "thermal mass", like the old trick of putting a lot of stuff in a furnace to keep the temperature more stable.
      So it's a different trick, but it looks like both tricks get the job done in a lot of cases. You'll see a very slow decline in temperature with the lumps of stainless steel and a steady temperature then a sharp decline with the phase change material. So long as you drin
      • by stevel ( 64802 ) *

        If by "lumps of stainless steel" you mean Joulies, you missed that the Joulies have phase-change-material inside - probably the same stuff as this mug. This is why I said it was the same trick.

      • I should have read more about these things since they appear to be wax filled lumps of stainless steel instead of just stainless steel.
    • These tests must be performed where relevant on both the mug, the lid and the mug with the lid.

      It must not loose more than 20 percent of the initial energy of the contained liquid for 1 hour.

      It has to survive a
      dishwasher
      washing machine
      dryer

      It must survive a 60 gravity impact on every facet on
      concrete
      steel
      tungsten
      tungsten carbide

      It must to survive the effects of a solid tungsten carbide cutting tool for 10 seconds.

      It has to survive all of this at -40, -20, 0 , 25 and 150 Celsius.

      At nominal room temperature i

    • by Anonymous Coward

      Joulies don't work [marco.org].

    • by Splab ( 574204 )

      Well I'm not good at them fancy maths, but for $40 I can get a mug or $60 I can get them beans...

      Now the beans might work for more than one mug, however, generally I only drink one cup of coffee at a time, so to me the mug seems to make more sense.

    • Doesn't anyone get the irony of a guy name Maxwell making Coffee?

      The best part of waking up is having Maxwell make your cup.
      Granted Maxwell coffee isn't the best coffee but still most of you growing up got the stupid song in your head.

  • by weilawei ( 897823 ) on Thursday December 12, 2013 @06:21PM (#45675141)

    The insulator – which Maxwell won't identify but swears is non-toxic

    I think this is a case where it most certainly needs to be disclosed in an MSDS and/or patent filing (though more likely in the MSDS, as the patent filing is allowed to be vague).

    • The insulator – which Maxwell won't identify but swears is non-toxic

      I think this is a case where it most certainly needs to be disclosed in an MSDS and/or patent filing (though more likely in the MSDS, as the patent filing is allowed to be vague).

      MSDS sheets aren't required for consumer products in most places in Canada. They're a workplace 'thing'.

      Nevermind the fact you can get an exemption for 'trade secrets'.

    • by ackthpt ( 218170 )

      The insulator – which Maxwell won't identify but swears is non-toxic

      I think this is a case where it most certainly needs to be disclosed in an MSDS and/or patent filing (though more likely in the MSDS, as the patent filing is allowed to be vague).

      I dunno. I have a Sigg insulated drink bottle, which holds 1L and if I pour hot green tea into it, it will still be hot the next day. Larges contributing factor in coffee cooling in a cup has to be surface area at the top. Evaporation takes energy with it, so minimize exposure at the top and your coffee will stay hot longer.

      Rather like those dang travel mugs where I can't drink the hot coffee for about an hour after I bought it >:(

      • I've never seen a Sigg bottle--do they also use a chemical insulator which changes phases and could potentially mix with the beverage? A bit of research on my part suggested that what DavidClarkeHR said is likely to also be true in the US, as consumer products are exempted from requiring MSDS's unless it's part of an employees function to handle some chemical. Amusingly, the FDA also states that any product emitting "any type of radiation" is under their purview. I wonder if they've ever heard of black-body
        • by icebike ( 68054 )

          If the material is separated from the beverage by the cup's inner wall, its not an FDA issue.
          It may be a CPSC issue if the inner cup was would bee thin enough to puncture easily (such as if you stir your hot chocolate), but there would seem to be no reason for a dangerously thin wall.

          • I wasn't saying it was an FDA issue, I was saying it was amusing and I stumbled across it in the course of looking for information.
    • IT'S PEOPLE! Temperfect mugs are made out of people!!

      .
  • by ackthpt ( 218170 ) on Thursday December 12, 2013 @06:24PM (#45675163) Homepage Journal

    It holds 800ml.

    If you need insulation, you are drinking it too slow.

    perhaps the ability to add an iv-drip

    • by Antipater ( 2053064 ) on Thursday December 12, 2013 @06:34PM (#45675277)
      Personally, the "cools it quickly to a drinkable temp" was the biggest attraction for me. I have to put a single ice cube in my mug when I use the coffee machine here at work, or else I have to wait twenty minutes so I don't scald myself.
      • by icebike ( 68054 )

        That would be a work place risk, probably already covered by OSHA.
        If you want to get everyone pissed off, just file an OSHA complaint. They will descend on your workplace and find fault with everything from the floor tile to the overhead lights.

        • by dj245 ( 732906 )

          That would be a work place risk, probably already covered by OSHA. If you want to get everyone pissed off, just file an OSHA complaint. They will descend on your workplace and find fault with everything from the floor tile to the overhead lights.

          Depends on the locality. I filed one against a summer employer for clearly unsafe activities. Common practice was to get in a clogged hopper with the conveyor underneath still running. The site supervisor advocated the practice. An extremely serious and obvious safety hazard. OSHA looked the other way.

          The company went bankrupt 2 months later.

      • This is the reason I drink my coffee with milk. Cuts the acidity just right, and also cools it to the perfect temperature.

        Another solution (for those that frequent coffee shops) is actually specifying beverage temperatures. When I go to starbucks, for example, I order my lattes at 140 degrees. Its a bit cooler than the normal, scalding temperature, and just right for drinking right away.
  • It's too tall and thin; it will tip over easily (not that it matters if it has a spill-proof lid, but still...).
  • by Anonymous Coward on Thursday December 12, 2013 @06:26PM (#45675187)

    A $40 coffee mug. Come here and let me slap you.

    • I would pay $40 for it, if I could use it to hold ice cold soda at around 35 degrees F. Is this thing reversible?

      • Unfortunately, it wouldn't work. In order to get what you want, you'd need to find a phase change material with a melting point of about 35 degrees F. And even then, it's unlikely to work since the beverage you'd be pouring into the mug would be already very close to 35F and as such, there wouldn't be much or any energy transfer between the beverage and the phase change material. But if you did get such a mug, you could store it in the freezer. Then the phase change material would freeze and when you used t

  • by Anonymous Coward

    I just need it hot enough until I finish drinking it.

    And having coffee sit around at 140 degree will eventually make it taste like shit.

    It's a cool design and invention, but it's one that should be applied somewhere else.

  • sounds ideal for /american style/ coffee; which has been criticised for being less than perfect. espresso anyone?
    • by Anonymous Coward

      coffee vs espresso is, frankly, a matter of taste. they're completely different drinks. that said, the cafe americano is an anachronistic abomination.

      and by 'american style', i'll assume you mean 'good'. american coffee culture has, by now, matched and surpassed the european in terms of quality, diversity, and most of all, snobbery, whether you want espresso or drip/french-pressed.

      • Having travelled through North America, this 'summer', it is possible to get decent coffee made from an Italian espresso machine. Just look for independent local cafeterias staffed by hipsters with beards. :) Pour overs have become a post-espresso fad.

        The secret is to 'have here'. Coffee-to-go is another story - if the store wraps your latte's disposal container in a cardboard sleeve to prevent hand scoldage then they're doing it wrong - 'experts' have remarked that flavour and nutrients in the milk are des

      • and by 'american style', i'll assume you mean 'good'. american coffee culture has, by now, matched and surpassed the european in terms of quality, diversity, and most of all, snobbery, whether you want espresso or drip/french-pressed.

        Ummm.. I take it you've never been to Europe?

        Espresso diluted with hot water being called an Americano is appropriate from a continental European standpoint.

        Over here, an espresso is the basis for coffee. If you want a powerful espresso they use less water, and you get a ristretto. If you want a regular cafe, you get a lungo. The serving of water is done right in the machine, and is whether the barista gives you a long or short "pull" (literally on old style machines you pull a lever to put water in a p

    • by Dahamma ( 304068 )

      Anyone can criticize anything, big deal.

      And this isn't ideal for "American style" anything. It's ideal for keeping a certain quantity of hot liquid hot. Feel free to fill it with a latte, cocoa, tea, apple cider, mulled wine, or your own urine if you feel so inclined.

  • Sunk cost (Score:5, Funny)

    by istartedi ( 132515 ) on Thursday December 12, 2013 @06:33PM (#45675265) Journal

    It'll never sell to me. There are sunk costs involved. I have too much engineering invested in non-linear coffee consumption as cheap mugs and paper cups lose heat. Slowly at first, with much intake of the aroma. Then cautious sips, then normal sips, then fairly heavy consumption somewhere between 1/2 and 2/3rd of the way down. It ain't broke. I'm not fixing it. It works anywhere. No need to buy an expensive mug, take it with me everywhere, wash it, and worry about losing it.

    • Re:Sunk cost (Score:5, Informative)

      by weilawei ( 897823 ) on Thursday December 12, 2013 @06:48PM (#45675377)
      A sunk cost [wikipedia.org] is something you walk away from. That's why it's sunk. It shouldn't influence your future behavior. Continuing to throw money at it is known as "throwing good money after bad".

      In economics and business decision-making, a sunk cost is a retrospective (past) cost that has already been incurred and cannot be recovered. Sunk costs are sometimes contrasted with prospective costs, which are future costs that may be incurred or changed if an action is taken.

      In traditional microeconomic theory, only prospective (future) costs are relevant to an investment decision. Traditional economics proposes that economic actors should not let sunk costs influence their decisions. Doing so would not be rationally assessing a decision exclusively on its own merits.

      Sunk costs should not affect the rational decision-maker's best choice. However, until a decision-maker irreversibly commits resources, the prospective cost is an avoidable future cost and is properly included in any decision-making processes.

      Evidence from behavioral economics suggests this theory fails to predict real-world behavior. Sunk costs do, in fact, influence actors' decisions because humans are prone to loss aversion and framing effects.

      • Economic theory be damned. I'm going all-in on ignoring their product.

  • by Hillgiant ( 916436 ) on Thursday December 12, 2013 @06:39PM (#45675315)

    The unnamed insulator is Spam. Not sure if that makes it toxic or non-toxic, though.

  • by Anonymous Coward

    Unless the "phase change" material is quite massive, making the mug heavy, there is no way that a thin layer can literally cool a piping hot drink enough to be useful, let alone act as a temperature maintainer. A well built thermal mug can also keep a hot liquid between 128 and 140F for 90 minutes. This smacks of a bit of a con. Well done, con.

    • The phase change material comes into equilibrium with the inner material, reducing the heat of the inner material (coffee) by moving some of it to the insulator. The two inner layers (coffe + phase change) are maintained in equilibrium by the outer insulating layer which appears to be traditional. Now, as for effectiveness, I'll let someone else spend the $40.
  • by Anonymous Coward

    My money is on Gallium:

    http://en.wikipedia.org/wiki/Gallium

    http://www.youtube.com/watch?v=aolRO9eteSk

    It melts at 30C and is actually non toxic. Maybe he alloys something with it to bump the melting point up a little, though, basic thermo tells me an alloy will melt at a lower temp.

    Anyway, there are variations on this that aren't so nicely non-toxic due to components like: tin, bismuth, antimony and lead.

    http://scitoys.com/scitoys/scitoys/thermo/thermo4.html

    • by thatseattleguy ( 897282 ) on Thursday December 12, 2013 @07:15PM (#45675593) Homepage
      All good, except; gallium is hella expensive. And very very dense, therefore very heavy.
      My money is on good old-fashioned paraffin wax, which (at least in the bulk candle variety that I bought in my hippie candle-making days) melts at exactly 140F.
      Cheap and food-grade (it coats many candy items) and pretty light.
    • Sorry, but a melting point of 30C is entirely too low. That's about 85F and that is the temperature that the cup of coffee would be soon brought down to until all of the gallium melted. The 140F ( 60C) temperature mentioned points towards paraffin wax which is commonly used as a phase change material for maintaining temperatures http://en.wikipedia.org/wiki/Paraffin_wax#Properties [wikipedia.org]

    • by dbIII ( 701233 )
      It's listed as a material that is in food so I'd say not.
      Heavily salted bacon grease? Coconut oil/Copha? Any ideas for something that's going to last and melts at 60C?

      As for basic thermo - look for a binary phase diagram for an alloy between two metals of different melting points. There will be some compositions where the melting point is higher than that of the one with the lower melting points. Tin-Lead is a good one to look for, you'll notice that with a lot of tin the melting point is higher than t
  • 90 minutes is not "hours." It's not even plural; it's less than 2 hours.

    • by JesseMcDonald ( 536341 ) on Thursday December 12, 2013 @07:18PM (#45675621) Homepage

      Any quantity over one is plural, including 1.5 hours. For that matter, while fractions between zero and one are generally written in the singular form (1/2 hour), the equivalent decimal forms are typically plural (0.5 hours). Zero is always plural. Really, the only quantity guaranteed to use the singular form is exactly one.

      That said, you're correct that the quantity-free "hours" would generally imply at least two hours, regardless of the fact that 90 minutes converted to hours would be written with a plural. That's because it doesn't include potential fractions of an hour, only whole numbers.

      • by Anonymous Coward
        Very well done, professor. Take the next couple of weeks off for Christmas. Happy Holidays.
  • Who needs that? Doesn't everyone on this site tend to slam the caffeine down as quickly as possible?
  • by Bacon Bits ( 926911 ) on Thursday December 12, 2013 @07:19PM (#45675627)

    My guess is the mystery insulator material is beeswax. At least, the temperatures are about right, it's non-toxic, and doesn't oxidize AFAIK.

  • Pfft... (Score:4, Funny)

    by Anonymous Coward on Thursday December 12, 2013 @08:23PM (#45676119)

    What a piker.

    Just line your coffee mug with plutonium. That'll keep it warm.

  • I just set my ceramic mug on top of my Apple Airport, that seems to keep it warm.

  • This is precisely one thing that irks me about living in the US. People get the coffee culture completely wrong, they even say things like "let's grab a coffee". In civilized countries, you never *walk* around with a coffee. You sit down, spend 10 focused minutes on an espresso and maybe conversation and then go on doing things with both hands. Walking around holding some significant fraction of gallon of coffee is just pointless - you get gorilla arm, you never enjoy coffee and you never enjoy a real break.

    • A slightly more subtle than glaringly obvious example of the No True Scotsman fallacy.
    • While I enjoy the same things you stated, I don't really see how you "can't take coffee seriously" if you ever do these things. As a working individual, there are times when I simply don't have the time to sit down and chat for a while. But I sure as hell would love to be able to have a hot cup of coffee as I walk to a meeting or something.
      • I think you clearly validated their hyperbole regarding U.S. work culture. As someone who is also pressured by work to a degree of questionable ethical limits, I'm a bit disappoint to see another person standing up for the work place culture that is demonstrably wrong (not entirely about the coffee thing, but with regards to hustle and bustle).
        • there are times when I simply don't have the time to sit down and chat for a while

          I really don't understand how one could interpret that to mean that I *never* have time to sit and enjoy a cup of coffee. Or whatever beverage I like. There are plenty of times at work where I'll take 10-20 minutes and enjoy a cup of green tea while just relaxing. But occasionally, I may have a meeting that I have to go, immediately following an hour or two of trying to work through some bugs in code. In that three hour block, I would like some coffee, but there aren't any breaks possible.

          Maybe you guys

    • I am also an espresso drinker, so I would not use it for coffee, but I see it could be useful for tea.
  • No cup of coffee should need to sit around more than 30 minutes. If you're doing hours of reading or socializing, you should be having more than one cup, sized appropriately to your preferences and tolerance.

    Hell, part of the social ritual is the host refilling the beverage, a demonstration of their ability to provide an abundance to a guest.
  • I'll never understand the fascination with beverage container designs that encourage spilling. Ever since getting a Highwave Hotjo [amazon.com] several years ago, I've been able to keep coffee (or masala tea more often these days) next to my electronics projects all day. Its shape resists spilling and it even has a nonskid mat on the bottom. I've had mine for, gosh, probably six or seven years and it's still as good as new.

    Temperature stability seems likle a great idea, but this vessel design only seems well-suited f

  • This is.

    From Cliff Stoll's Acme Klein Bottles

            mark "wish it wasn't quite that expensive...."

    • by whitroth ( 9367 )

      Right, forgot slashdot edits URLs... Notice spaces before www....

      http:/ [http] /www.kleinbottle.com/index.htm
      and the mug, er, "Klein Stein"
      http:/// [http] www.kleinbottle.com/drinking_mug_klein_bottle.htm

  • Wax has been used for phase change cooling for quite some time. Any ways, a wiki link: http://en.m.wikipedia.org/wiki/Paraffin_wax [wikipedia.org] And, a table of (candle) wax melting points: http://www.nuscentscandle.com/melt-point-and-pour-candle-wax-temperature-chart/ [nuscentscandle.com] You just have to account for the expansion, as always.

Two can Live as Cheaply as One for Half as Long. -- Howard Kandel

Working...