Rainy day firing

[CactusPots]

I finally got a long held desire.  I know some of you will laugh, but I've always wanted to fire on a rainy day.  It doesn't rain much in Southern California.  It's pretty much winter rain only and I've been on a 3 glaze fire schedule for the year until this year.  Looks like we'll have an exceptional rainy season this year.  Rained gang busters most of the day.

I've always thought that firing in the rain would give a better firing.  Any opinions on that?   Maybe more oxygen in the air.  We'll see tomorrow when I open up, but I loved the ambiance.  Had to chase multiple leaks all day   I'm more set up for shade than run off.  Good day though.  Loved it.

[oldlady]

always interesting to hear about the differences we all experience.   spraying glaze under the garage roof overhang on a rainy day is not a lot of fun but it can be done.  as long as the rain is from the other direction!

[liambesaw]

Probably different in socal, but I fire mostly in the rain.  The thing I hate is that it can take days to glaze because of the humidity.  The firing doesn't take longer or do anything different, but the heat causes a bunch of water vapor form and condense on everything in my carport.

[JohnnyK]

Started a glaze firing this AM in northern CA on a rainy day after a 3" rainy weekend. Don't expect any problems here. I glaze in a warm, dry house and transfer to the garage with the pots covered...run a long Ramp1 and should be able to open the kiln tomorrow morning with all the pieces for a $350 sale...

[Min]

Couple weeks ago the roof over my kiln area had a leak. We have a lot of rain here and the drip picked the worst place to leak through, right above one of the controllers.  Fixed the roof and replaced the controller with an old one I had, you could say it was a rain of chaos as this was right at a super busy time and I needed the kiln for bisque.

[CactusPots]

I have enough covered patio and indoor workspace that glazing isn't a problem.  I'm not really sure why glazing would be a problem unless you're actually in the rain.  Drying to ready for bisque on the other hand...  I'm not used to much rain, so I'm not patient with slow drying when I'm ready to final dry.  The bisque is all in an electric kiln inside, the propane downdraft is outside under a cover.  No actual leaking on the kiln itself, plenty on the patio under the kiln.  I'll probably unload tomorrow afternoon.

It seemed to me like the kiln had an easier time climbing today.  I went from stone cold to 450 in about an hour, faster than usual.  It's hard to say if the rain had that effect, or just my heavy hand on the gas.  I never lost the hour I gained with that early climb and finished an hour earlier than usual at 11 hours.  At finish it looked like a hard 10 on top and a soft 10 on the bottom.  Probably get a little more heat work after that.

[liambesaw]

When it's raining and I'm spraying and dipping glaze, the glaze takes forever to dry.  In the summer I can dip and spray and the glaze dries real quick, this time of year I have to wait a day or two between dipping and spraying or it'll just puddle and slough off.

[Rae Reich]

4 hours ago, CactusPots said:

I have enough covered patio and indoor workspace that glazing isn't a problem.  I'm not really sure why glazing would be a problem unless you're actually in the rain.  Drying to ready for bisque on the other hand...  I'm not used to much rain, so I'm not patient with slow drying when I'm ready to final dry.  The bisque is all in an electric kiln inside, the propane downdraft is outside under a cover.  No actual leaking on the kiln itself, plenty on the patio under the kiln.  I'll probably unload tomorrow afternoon.

It seemed to me like the kiln had an easier time climbing today.  I went from stone cold to 450 in about an hour, faster than usual.  It's hard to say if the rain had that effect, or just my heavy hand on the gas.  I never lost the hour I gained with that early climb and finished an hour earlier than usual at 11 hours.  At finish it looked like a hard 10 on top and a soft 10 on the bottom.  Probably get a little more heat work after that.

We SoCal potters are lucky that for most of the year freshly glazed pots dry so quickly. My sympathies to all those who live in high humidity. When I worked down by the beach, glazing on foggy mornings, we put the drying glazeware into the still-warm kiln to help speed the work and, further inland, the kitchen stove on low,

Rainy day ^10 firings with an outdoor manual gas kiln are sorta thrilling. Before we built the kiln shed around it, my kiln was mostly covered by a tarp between firings but inevitably got a bit wet. The damp hard brick steamed a lot as the kiln heated up, dried pretty fast and then created its own aura of heat that evaporated rain before it could reach the brick! You could stand two or three feet away from the kiln and be dry on the kiln side and wet on the away side.

I have often thought that the difference in barometric pressure between dry days and rainy days would have an effect on firings. @Bill Kielb, you have any idea if this should be so? (Guess I'm mostly referring to gas firing.)

[neilestrick]

Back when I was in undergrad, the old Alpine updraft would fire about an hour faster on rainy days. I don't know if it's because of the moisture in the air or the barometric pressure, but it was definitely a real thing because that kiln was always fired with the same settings.

[CactusPots]

I'm trying to think if I've ever done glazing on an actual rainy day because I've never noticed an issue with glaze not drying.  I do multiple dips of different glazes on a lot of pots.  The second coat can't be applied before the first is dry to touch.  It seemed to me the water was absorbed into the bisque (cone 06) rather than evaporated off the pot.

Would not the water content in the air increase the oxygen content?

[neilestrick]

I've been researching this all morning. Water vapor is not easily combustible (which we know- water doesn't burn), so the oxygen in it does not contribute to combustion. Moist air is less combustible than dry air because the water vapor is taking up space in the air and making it less oxygen rich. That makes total sense, because if it did improve combustion we'd be pumping water vapor into our car engines and home furnaces. And the kiln is not hot enough to break apart water molecules and have the individual elements contribute in any way. So if anything, gas kilns should be less efficient on a rainy day due to the extra water vapor. Apparently drag racers are very aware of this, because as the humidity rises the efficiency of their engines goes down, which lowers their speed/acceleration.

So that leaves barometric pressure. In theory, low pressure rainy days should further reduce combustion efficiency, since lower pressure means air that is lower in density and therefore lower in oxygen per volume.

So all signs point to a kiln firing slower on a rainy day, but that was not my experience at all. But maybe it's not just about the combustion. Firing a gas kiln is not about pumping heat into the kiln and holding it there. It's all about pumping hot air in, transferring to the ware, moving that cooled air out, and replacing it with more hot air. Flow is everything. Kilns that aren't reaching temperature or are firing unevenly often have flow problems. That's why the little round top loading gas kilns have so many problems- the air can't move through them properly. So in regards to rainy days, I'm thinking that the lower barometric pressure somehow affects the flow in a beneficial way.

[Hulk]

For sure elevation matters for available oxygen.

I watch the weather closely (bicycle nut; temperature, wind, and rain matter!), but not so much the barometer - the prediction/model, doppler radar and satellite imagery I'm watching closely. That said, Wikipedia says wet weather is associated with low barometer, hence lower partial pressure of oxygen, hrrm. One might believe that air becomes denser as the temperature drops; that's what I have believed.

Humidity, for a gas kiln, don't believe there's any phase change, vapor is vapour (same in Canada, Australia, UK as USA, just spelt different), hence, likely not related to oxygen. As radiant heat trumps convection (per the kiln pundits), and what I'm finding for humidity and convection being a bit dense reading,  skippin' that for now. I don't believe the water vapour is "cracked" via typical (e.g. a typical gas flame) combustion - water is one of the products of (typical) combustion.

Does your flame path draw better when it's cool out? Gas firers, do you adjust your settings for wet days?

...good question!

Everything else (seemingly) equal, warm days are faster onna bike; I'd like to think it's because the air is thinner. Cool day fly balls are home runs on warmer days...

Just read Neil's post; higher humidity, less O2? Every day, opportunity to learn, "If humidity is disregarded during calibration, the final error can be as high as around 3%. That is a good reason to think about the RH of ambient air during calibration." from:

https://www.elscolab.com/nl-en/news/dont-underestimate-the-influence-of-relative-humidity-on-your-oxygen-measurements

[neilestrick]

41 minutes ago, Hulk said:

Just read Neil's post; higher humidity, less O2? Every day, opportunity to learn

It my be that there's a total higher amount of oxygen in a given volume of air when the percentage of water vapor is higher, but the oxygen in the water vapor is not useable. We can't burn it, we can't breathe it. It's just taking up space, displacing air that does have useable oxygen. So in terms of useable oxygen, which is what we need for combustion, more humidity equals less oxygen.

[Bill Kielb]

On 12/5/2019 at 2:35 AM, Rae Reich said:

We SoCal potters are lucky that for most of the year freshly glazed pots dry so quickly. My sympathies to all those who live in high humidity. When I worked down by the beach, glazing on foggy mornings, we put the drying glazeware into the still-warm kiln to help speed the work and, further inland, the kitchen stove on low,

Rainy day ^10 firings with an outdoor manual gas kiln are sorta thrilling. Before we built the kiln shed around it, my kiln was mostly covered by a tarp between firings but inevitably got a bit wet. The damp hard brick steamed a lot as the kiln heated up, dried pretty fast and then created its own aura of heat that evaporated rain before it could reach the brick! You could stand two or three feet away from the kiln and be dry on the kiln side and wet on the away side.

I have often thought that the difference in barometric pressure between dry days and rainy days would have an effect on firings. @Bill Kielb, you have any idea if this should be so? (Guess I'm mostly referring to gas firing.)

We could calculate it , it surely does have an effect . Primary air is a significant load on the kiln and small density changes likely would present a load. Pretty easy to approximate, I will add it in to the temp calc which was a question that when it was cold outside how much does that affect the firing.

Water vapor will have an effect but my guess is it will be in the form of enthalpy or more btu per pound to heat it to flame temp, but maybe not.  Since we are talking enthalpy difference , humid air will contain more energy and water  does take up space so from a percentage standpoint a lower percentage oxygen but firing a gas kiln requires an approximate 10:1 mixture which actually wastes fuel somewhat with excess oxygen and makes our firing efficiency go down but is also safe in that there is excess air.

so humid days can be more efficient but also can take more overall energy. Lots of numbers to include. We shall see what they tell us.

Sorry keep getting interrupted! The curves below show O2 percentage is exponential vs temperature which is linear which could mean lowering 02 to a more efficient point could actually save more energy since most burners operate with excess air for reasons of safety, however kilns really don’t come with 02 trim so they likely were designed with more excess air than necessary.

so I would  say it is entirely possible that on rainy or humid days lowering the percentage 02 could result in increased firing efficiency.