PeterH

Oops, I was completely mislead by the controller's manual stating that "the controller will display PF when first plugged into an outlet".  Especially as elsewhere it clearly indicates that the switch should be in the off position between firings.
Apologies to the OP @socrasoup
 

My reading is the on / off switch was turned on, else there would be no PF display and it would be blank. I think the “safety” switch referenced is the on / off toggle switch.

The elements of the US version are all the same, 11.4 ohms. However, because the middle and bottom elements are wired in parallel, for a service person taking a resistance reading across either of these two with everything in situ will include the other, yielding a reading of half, or 5.7 ohms.

I have boards made as in that video above.
First you need a base board.  Then decide what the tallest size you will need.  Then make the length of the boards so you can clamp them and they still fit on your base board.
I've also used cardboard boxes, fruit boxes, tupperware containers, anything that will hold the weight of the plaster, or can be lined with bin bags and padded out with cardboard, foam, anything.  Usually I'm restricted by height more than any other dimension.

Pure & Simple suggest https://cdn.shopify.com/s/files/1/1130/0194/files/INSTRUCTIONS_2021.1.pdf?v=1609298598

Depends how large the molds will be but they are adjustable to be smaller. I like using roofing flashing (for cylinder shaped molds) that comes in different lengths from a hardware store. I tape up the seam with duct tape and seal the bottom where it sits on the table with soft clay coils made from waste clay. If you cut a long piece it is also adjustable and reusable.
 

For now might I suggest the simple view that the tin is essential for copper reds and it is chemistry ………not colorant. If you accept that then reduction is simply attained by a really dirty carbon monoxide rich atmosphere with very little oxygen to reoxidize things so to speak.
From there most all reduction is a combination of reducing things to create a color or carbon trapping for effect. So my most consistent Raku pieces were reduced in a bucket lined with plain old newspaper, inverted in a tub with a few inches of water to seal out air. Once I figured that out it was much easier to compare recipes and changes. Dead leaves, organics ……… I found newspaper did the job consistently just fine.
So the common reducibles: copper, iron, tin (with copper, prox 3:1), nickel, cobalt and manganese. Common effects: reduction colors, iron acts more as a flux and turns black, carbon trapping, crackle (a glaze flaw) and horse hair etc….
Experimenting is still one of the best ways to learn though, for sure.
I have spent a lot of time getting smooth reduction from all parts of a kiln. Even reduction that does not reoxidize is very important in kilns and Raku. Don’t let air in is what I learned and copper red is a decent indicator of how you are doing.

Linda Arbuckle adapted Daniel Rhodes slip and engobe recipes below. I would see if you can get the materials for the Cone 04 Wet recipe in the first column.
Are ceramic frits available to you in Iran? Any chance you can get Ferro 3134? If not can you get borax? It is often sold as a laundry cleaner. If you can get borax (but not the frit) swap 5% borax for the frit and dissolve it in really hot water and try a test with that. Don't make a big batch without testing it on your clay first. Get the engobe onto the clay as soon as you can. The drier the clay the more chance it will crack or flake off during drying and firing.
To make white you will need to add an opacifier, can you get any zircon based ones? You could use tin but it's much more expensive. Without the opacifier the engobe will still be white but not as opaque a white as with the opacifier. If you use tin use 1/2 the recommended amount of zircon opacifier called for in the recipe.
If you want other colours of engobe this link has the original recipes plus some colourants for other colours.
(I'm going to move this thread over to the chemistry section)

 

The thing about only using as a body stain is something you can just ignore. I use stains a lot, hence planning on using the black stain to fill in the low texture and make the whole thing look darker, but I could definitely take a small portion of glaze and mix some black stain into it and see if it darkens it. No harm in that and I would learn something useful whether or not it works. I have never heard of anyone darkening a commercial glaze with stains, but with studio glaze recipes people will mix oxides and stains to achieve certain colors, so I think it has a chance! If it doesn’t work, or does but just doesn’t look that great, I know the three firing method will work so since no one else but you has come up with another way to try, I will just bite the bullet and fire three times, but fill up the kiln as much as possible with bisque or test tiles so it isn’t getting wasted, and possibly firing it a little bit hotter at cone 04 instead of 06 may even make the teal darker as well. I have seen teals get much darker, almost black, when going from 06 to 6, and while 06 to 04 isn’t too much of a change it is at least a little hotter. Thank you for the idea.

Would  adding an "inert" stain to the commercial glaze serve your purpose?
I suspect stains consisting of spinel pigments would be suitably inert, although obviously check the small-print.
For example Mason 6600 best black  6600 https://www.masoncolor.com/ceramic-stains/blacks/6600-best-black).
reference notes https://www.masoncolor.com/reference-guide

>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>^^^^
                                  

Don't know how serious the advice "Use only as a body stain" is. For example
https://www.scarva.com/en/gb/Mason-Stains-By-Mason-Color-6600-Best-Black-Stain/m-2170.aspx
Our range of Mason colours with over 60 ceramic stains can be used in a wide variety of cost-effective applications. All stains in this revolutionary new colour system contain NO LEAD and can be used as glaze stains ...

 

Nice discussion on copper/tin interactions in
Copper Red Glazes https://digitalfire.com/article/copper+red+glazes
Well worth reading the whole page, but the highlight is perhaps
Sn does a couple things. First it improves the solubility of Cu. Metals, per se, aren't really very soluble in glaze and if you can't get the metal dissolved, it can't very well be precipitated in any organized fashion. Second, on cooling, Cu tends to attract Sn atoms from the glaze. These atoms sort of "coat" the crystals as they are developed and thus serves to control their size by limiting the attachment of further Cu atoms to the crystal. This behavior is that of a protective colloid and it is of great advantage. Because if the crystals get big, the glaze turns "livery" looking, and the doughnut remains elusive. Third, to the extent that Sn has limited solubility in SiO2 or B2O3 based glassy material, it probably also serves to provide nuclei on which the coloring crystals can grow.
Tin oxide is added to all practical non-lead Cu red glazes in amount way beyond what's necessary to promote good solution of Cu in the glaze - many compositions contain up to 4-wt%. Of course, if there's too much tin it doesn't all dissolve -- causing opacity. This may or may not be desirable.
 
Also of possible interest
The Dual Mechanisms of Tin Oxide in Copper Red Glazes https://glazy.org/posts/168150

It’s not the last hour, you fire at the rate of 60c PER HOUR for the last 100c so that will take a little more than 1 hour and a half (1:40 actually). With respect to cones, they are made of glaze and calibrated to show accumulated heat work which happens mostly in the last 100c This is where glaze mostly matures. Silica and alumina without flux don’t like to really melt below about 1600c flux helps things melt. The question becomes when?
Because cones are glaze and glaze melts as a result of fluxes lowering the melting point and time and temperature affects accumulated work, cones more accurately show when a glaze is mature. Because they are made of glaze and calibrated to bend at their cone value.
Think of it a little like cooking, if you leave your pizza in the oven and ignore time and cook it for 30 minutes more than the instruction, it’s probably well over done. Time and rate combine as something called heatwork. Cones are made of glaze and indicate accumulated heatwork on a glaze.
Here is an interesting thought, if I reach 1031c and hold or soak for thirty minutes I now drive this from cone 05 to likely two cones higher in accumulated work or cone 03. Time And temperature affect glaze maturity.
So to answer your last question, cones indicate what happens in about the last 1h40m of the firing, which is the most important part of the firing with respect to maturity.

Nice discussion on copper/tin interactions in
Copper Red Glazes https://digitalfire.com/article/copper+red+glazes
Well worth reading the whole page, but the highlight is perhaps
Sn does a couple things. First it improves the solubility of Cu. Metals, per se, aren't really very soluble in glaze and if you can't get the metal dissolved, it can't very well be precipitated in any organized fashion. Second, on cooling, Cu tends to attract Sn atoms from the glaze. These atoms sort of "coat" the crystals as they are developed and thus serves to control their size by limiting the attachment of further Cu atoms to the crystal. This behavior is that of a protective colloid and it is of great advantage. Because if the crystals get big, the glaze turns "livery" looking, and the doughnut remains elusive. Third, to the extent that Sn has limited solubility in SiO2 or B2O3 based glassy material, it probably also serves to provide nuclei on which the coloring crystals can grow.
Tin oxide is added to all practical non-lead Cu red glazes in amount way beyond what's necessary to promote good solution of Cu in the glaze - many compositions contain up to 4-wt%. Of course, if there's too much tin it doesn't all dissolve -- causing opacity. This may or may not be desirable.
 
Also of possible interest
The Dual Mechanisms of Tin Oxide in Copper Red Glazes https://glazy.org/posts/168150

Nice discussion on copper/tin interactions in
Copper Red Glazes https://digitalfire.com/article/copper+red+glazes
Well worth reading the whole page, but the highlight is perhaps
Sn does a couple things. First it improves the solubility of Cu. Metals, per se, aren't really very soluble in glaze and if you can't get the metal dissolved, it can't very well be precipitated in any organized fashion. Second, on cooling, Cu tends to attract Sn atoms from the glaze. These atoms sort of "coat" the crystals as they are developed and thus serves to control their size by limiting the attachment of further Cu atoms to the crystal. This behavior is that of a protective colloid and it is of great advantage. Because if the crystals get big, the glaze turns "livery" looking, and the doughnut remains elusive. Third, to the extent that Sn has limited solubility in SiO2 or B2O3 based glassy material, it probably also serves to provide nuclei on which the coloring crystals can grow.
Tin oxide is added to all practical non-lead Cu red glazes in amount way beyond what's necessary to promote good solution of Cu in the glaze - many compositions contain up to 4-wt%. Of course, if there's too much tin it doesn't all dissolve -- causing opacity. This may or may not be desirable.
 
Also of possible interest
The Dual Mechanisms of Tin Oxide in Copper Red Glazes https://glazy.org/posts/168150

Nice discussion on copper/tin interactions in
Copper Red Glazes https://digitalfire.com/article/copper+red+glazes
Well worth reading the whole page, but the highlight is perhaps
Sn does a couple things. First it improves the solubility of Cu. Metals, per se, aren't really very soluble in glaze and if you can't get the metal dissolved, it can't very well be precipitated in any organized fashion. Second, on cooling, Cu tends to attract Sn atoms from the glaze. These atoms sort of "coat" the crystals as they are developed and thus serves to control their size by limiting the attachment of further Cu atoms to the crystal. This behavior is that of a protective colloid and it is of great advantage. Because if the crystals get big, the glaze turns "livery" looking, and the doughnut remains elusive. Third, to the extent that Sn has limited solubility in SiO2 or B2O3 based glassy material, it probably also serves to provide nuclei on which the coloring crystals can grow.
Tin oxide is added to all practical non-lead Cu red glazes in amount way beyond what's necessary to promote good solution of Cu in the glaze - many compositions contain up to 4-wt%. Of course, if there's too much tin it doesn't all dissolve -- causing opacity. This may or may not be desirable.
 
Also of possible interest
The Dual Mechanisms of Tin Oxide in Copper Red Glazes https://glazy.org/posts/168150

Only hand-waving, but I expect the importance of tin (and iron) in some copper glazes is because all three elements have variable valencies; and in the right circumstances can help redox reactions  move copper from Cu(II) to Cu(I) or even Cu(0) -- and/or buffer it against oxidation once it's in the desired state. There is also Weyl's point that the presence of tin increases the solubility of metallic copper in a glass (or glaze), which can be important in obtaining colloidal copper particles.
Woldemar A. Weyl Coloured Glasses has some interesting thoughts on the colouring mechanisms in glasses. Not cheap, but if you can  borrow it on an interlibrary loan ...

Only hand-waving, but I expect the importance of tin (and iron) in some copper glazes is because all three elements have variable valencies; and in the right circumstances can help redox reactions  move copper from Cu(II) to Cu(I) or even Cu(0) -- and/or buffer it against oxidation once it's in the desired state. There is also Weyl's point that the presence of tin increases the solubility of metallic copper in a glass (or glaze), which can be important in obtaining colloidal copper particles.
Woldemar A. Weyl Coloured Glasses has some interesting thoughts on the colouring mechanisms in glasses. Not cheap, but if you can  borrow it on an interlibrary loan ...

Change this search to your location & currency. Cheapest 2nd hand here is £232!
https://tinyurl.com/2p4k2jst
Does your country have an inter-loan library system?
I've no idea if the sign-up ebook services or are real or scam., but a google for ash glazes phil rogers pdf turns up
http://infinity.wecabrio.com/080198243X-ash-glazes.pdf
... and a thesis by somebody else on glazy
https://wiki.glazy.org/uploads/default/original/1X/085b890dabdd507a348fdcc09e4247b954029145.pdf
Posts for wood ash on glazy at https://glazy.org/?keywords=wood ash
... including a Stull Chart
 

I doubt it, but am not in a position to know.
However you would only be using it to seal the unglazed edge of the collar, which would presumably not be in contact with the soil. Minimising any opportunity to leach.

I get similar freeze/thaw cycles here in Calgary. We’re high altitude too. 
I think the risk from water absorption on a clay fired to maturity is much less than water accumulating within the ring in a puddle from melted snow. I had some soda fired stoneware planters that lasted for 15+ years outside, until one year I left it right side up and it collected snowmelt. If it was me, I’d put the glazed side down into the earth, not worry too much about the unglazed rim, and keep water from accumulating inside the ring during the winter somehow. 

John Britt has the book on his website:
The Quest for the Elusive Leaf Bowl and other Selected Articles
I just realized the title is actually using "Illusive" but I'm pretty sure he meant Elusive, as in hard to track down rather than "illusory" or false.
I also just learned that John Britt is from my neck of the woods (Ohio, Daytonish).  I haven't lived there since the late 80s, but still.

I don’t think the artist who made the pot in your supplied image is applying overglaze: I think they’re just putting a leaf on a glaze that’s got the right chemistry to be inclined to turn that gold colour when the ash from the leaf melts into the right spot. Some of the colour response is going to come from the change in the fluxes in that really localized area, and some of it would come from the additional iron, chrome and manganese. And phosphorous. 
Joe at Old Forge Creations did this blog post last September about some chemistry explorations he did with a black tenmoku recipe that formed yellow crystals. He was fine tuning the rate of iron crystals by altering the amount of magnesium and calcium. There’s more, but that’s the Cole’s notes version if you don’t want to read the blog. If you look at the image in Peter’s reply just above mine here, you can see that there are tiny yellow specks in the glaze, meaning that one is probably already susceptible to turning that particular gold colour. Adjusting the localized chemistry with ash from a botanical that contains magnesium is enough to push the glaze in the right direction. Could happen in either oxidation or reduction I would think. 

An interesting spin-off?
I welcome others interpretation of this paper (pity it doesn't have a pictures)
 Research on the New Woodleaf Glaze in Celadon
https://www.scitepress.org/Papers/2019/85615/85615.pdf
The image on a good leaf bowl is notable both for its fidelity and its colour.

https://www.yuyinghuang.com/shop/mulberry-leaf-tenmoku-teabowl
This paper thinks of the leaf as a way of applying an over-glaze image to the pot. It starts by analysing the mulberry leaf ash as it is heated, and comes up with a glaze formula:

Any thoughts on the colouring mechanism? And is it a property of the overglaze alone, or a reaction with the base-glaze?
It then considers the use of this overglaze which it uses with a celedon base-glaze.
Combine with celadon's mud glaze to make no less than 6 sets of test pieces, (I'm not sure if it is applied it as an overglaze, or mixed it with the celedon.)
 ... and then looks at the effect of firing temperature. Pity there is no pictures.
PS It would be interesting to know the analysis of the ash of other leaves traditionally used for leaf bowls.

222 page thesis
TRANSFORMATION OF SIX LEAVES GLAZE TO CONTEMPORARY CERAMIC BASES ON THE TAOISM CHARACTERISTICS
https://tinyurl.com/4a48pyky
In the research process, 768 glaze recipes have been tried. A total of more than 600 kilns have been fired, and more than 20,000 pieces of products have been fired. In the early stages there were a high probability of failures. However,
the rate of finished products finally increased from 2% to 80%

222 page thesis
TRANSFORMATION OF SIX LEAVES GLAZE TO CONTEMPORARY CERAMIC BASES ON THE TAOISM CHARACTERISTICS
https://tinyurl.com/4a48pyky
In the research process, 768 glaze recipes have been tried. A total of more than 600 kilns have been fired, and more than 20,000 pieces of products have been fired. In the early stages there were a high probability of failures. However,
the rate of finished products finally increased from 2% to 80%