PeterH

It depends.....  Some people are heavier appliers than others.  Commercial glaze usually says apply 3 coats.  I have seen people apply three coats that look like my 1 coat, and others whose 3 coats would puddle all over the kiln shelf.
At our community centre, I get newbies to do a "number of coats" test tile, before they do any glazing or underglazing.  A square tile of clay, marked into 4 smaller squares.  Corner 1 gets one coat of underglaze, corner 2 gets 2 coats, corner 3............etc
This gets bisque fired and then they apply 1 coat of clear on half of corner 1, 2 coats on half of corner 2..........
Second fire to earthenware, (we don't do any high-fire) then they (I) can determine if they are a light applier or a heavy applier.  This gives them a guide for future applications.    
We often repeat with a vertical tile with texture.

@PeterH Copper Oxide gives me dark specks. The carbonate is much more finely milled and gives a more uniform colour
@Min good to know. I might go the non cadmium green and mix it with black and a pinch of blue to get a more emerald green. I’m too scared of poisonous cadmium!

Useful reference
Amps vs. Volts vs. Watts vs. Ohms: What’s the Difference?
https://www.familyhandyman.com/article/electrical-terms-explained-watts-volts-amps-ohms-diy/
... with a good summary





 

If I was going to try to get a similar effect and I was using moulds, there’s a couple of ways to go about it.
You could start with thin layers of the light coloured slips to line the mould, possibly  brushed or airbrushed on unevenly, or even just very thin pours (2-3 minutes each). Next, there’d be a layer of black slip, and then do the full cast with the unpigmented casting slip. Once the piece is removed from the mould, it looks like some kind of abrasion happens, whether through using a trimming tool or a metal rib to scrape off some layers, or sanding as others have mentioned. I’d be more inclined to do that work when the piece is firm leather hard to reduce dust creation than to sand, but I hate wearing a respirator more than strictly necessary. 
Because it looks like she’s slipcasting a textured cup and then layering other colours on top, it looks like she’s putting a black slip or underglaze layer over the whole piece, and using 2 other layered complimentary colours (yellow and orange, blue and green, pink and red) over the black. After that, again some form of uneven abrasion. 
There’s a few artists that layer coloured slips in the mould and do different things to reveal the layers. 

Two ideas you may find useful.
1) Stain the cracks to make them more visible (you may have more than you think).
2) Use a thermal stress-test to make "latent" cracks appear sooner.
... one from Digitalfire https://digitalfire.com/test/iwct
 
 

Found the image below on her book of faces page. Maybe u.g. on the slipcast textured blanks then wiped, sanded  or scraped down?

Textured clay, black , colour, sand down bumps leaving white?

Not saying this is her method but I think I would just texture the clay and paint the designs with underglaze. Clear glaze over the top might even get me some minor movement especially if sequenced to encourage.

Where there is a very slight difference in COE, a thicker glaze might show a crack where a thinner layer wouldn't (depending on some associated factors...).
COE is fundamental to combating crazing!
Materials expand and contract as they heat up and cool down, respectively.
Where clay and glaze expand and contract at rates that are different (enough), problems happen!
At one extreme, bits of glaze pop off the work, shivering, and at the other extreme, the glaze cracks, crazing.
Crazing can be ameliorated by changing the glaze formulation/composition, also by using a different clay.
You'll hear and read the term "fit" and "glaze fit" - where the glaze "fits" the clay, there aren't shivering or crazing problems.
Here's links to some articles:
Co-efficient of Thermal Expansion (digitalfire.com)
Glaze Crazing (digitalfire.com)
...and a few threads from this Forum:
Crazing Clear Glaze - Clay and Glaze Chemistry - Ceramic Arts Daily Community
Crazing question - Clay and Glaze Chemistry - Ceramic Arts Daily Community
The cracking depicted in the OPs image (first post, above) seems a special case to me - typical crazing forms a pattern, where a large pattern indicates a closer match than a fine pattern. I'm curious to know if the clay is cracking, or is it the glaze?

Weight if dry ingredients are involved.
But volumetric mixing (of made-up glazes) for test-tiles is a great idea ... providing you use a syringe with a decent scale.

@Jmvelezz Finally ...
Transformation of Six Leaves Glaze to Contemporary Ceramic Bases on the Taoism Characteristics
http://ithesis-ir.su.ac.th/dspace/handle/123456789/2977
... click on  60155902.pdf near the bottom of the page.
... which seems to be link to  http://ithesis-ir.su.ac.th/dspace/bitstream/123456789/2977/1/60155902.pdf
... which looks like the same link that doesn't work when you use it directly!
I've not found any English-language page at the university that would let me report the problems to the universities IT department. I suspect that they have got their permissions in a twist.
PS You may want to remove the watermark before printing. How to do it depends on your system. Start with a google for something like print pdf without watermark. Don't have the file any more, but think I uncompressed the pdf file then edited it directly (on Linux possibly using pdftk & vi).

If your piece is sculptural or decorative, there’s no problem with using your non-yellowing varnish. 
While I’ve seen some instances of copper washes or copper based raku glazes re-oxidize and change colour over time, they don’t fade.  I’ve not seen it happen with iron based pigments however.
Worth noting that raku artists who know about this phenomena will varnish their pieces to prevent it. 

A little googling if it's of any help.
This seems to be the video, and readers comments about the email address being non-functional.
https://www.youtube.com/watch?v=VC0QXALQT_M
A discussion
https://cone6pots.ning.com/video/home-made-slab-roller
Another users experiences
http://mudismymedium.blogspot.com/2012/04/slab-roller.html
... which comments on the non-functioning email & web references, and gives
https://www.biggovtsucks.com/docs/SlabRollerModified.pdf
https://www.biggovtsucks.com/docs/SlabRollercuttingchart.pdf
Good hunting!
PS A thread on a different DIY roller, with some comments that seem relevant.
 

If I remember correctly there is a video somewhere of making a Vertical slab roller also, 
best,
Pres

Hi colormek8art,
Welcome to the Forum!
Wow, that kiln looks to be in good shape.
While waiting on responses, could you confirm the phase requirement; is it three phase?
Also curious, what are the amperage and max temp ratings?
To test/run safely, the wiring must be proper.
The max temp rating could be important; what temperature target/range do you work in?

... or perhaps not.

Electroplating vs Electroforming: What’s The Difference?
https://facfox.com/docs/kb/electroplating-vs-electroforming-whats-the-difference

Electroforming
https://en.wikipedia.org/wiki/Electroforming
The process involves passing direct current through an electrolyte containing salts of the metal being electroformed. The anode is the solid metal being electroformed, and the cathode is the mandrel, onto which the electroform gets plated (deposited). The process continues until the required electroform thickness is achieved. The mandrel is then either separated intact, melted away, or chemically dissolved. ... my emphasis
PS Note that when the form is to be separated from the mandrel it is advantageous if the electro-deposited layer is only weakly attached to the mandrel. For electroplating strong adhesion is desirable.

If you find a potential image is there any way of getting a preview of how it will look when fired as a transfer (which will typically have a different resolution and pigment model)?

Sounds like a lovely idea. I think, though, that pot making and landscape painting are not often found in the same person! 
Assuming you have a few local artists who already do plein aire paintings of your area, you could ask if they would give permission to use their images for a limited edition run of ceramic decals that a local, or even an Etsy-sourced potter could apply to their dinnerware. (Be sure to also get some practice, generic decals for the potter’s firing calibration tests, for best possible results.)
Alternatively, there may already be images of your favorite areas that do not require copyright to reproduce.
I think there have been several references to ceramic decal makers in past posts, but an internet search should lead to Custom Ceramic Decal Maker. 
 

Tough question!
Parian* is generally defined as a "self-glazing porcelain" which appears to have nearly zero absorption.
How are you using Parian?
Do your finished wares absorb water, at all?
 
*Composing a Workable Parian Clay Body (ceramicartsnetwork.org)

Example of cobalt concentration vs depth of colour
Cone 6 Ultramarine Cobalt Blue Glaze (Glossy Clear plus Cobalt Carbonate)
https://www.thestudiomanager.com/posts/cone-6-ultramarine-cobalt-blue-glaze-glossy-clear-plus-cobalt-carbonate

Tst
... but it doesn't have the cyan-ish tinge.

No, I think my math. Assuming 8”round prox. 20.32 cm so area should by 3.14x((20.33/2)^2 ) = Prox 324 sq cm. So 22W (from above)/ 324= ..068W per sq cm. A bit more than your floor heater ought to melt ice off your mirror as opposed to heating a floor to comfort temps.. I think you are in range and my quick calcs are wrong above.
All done flipping back and forth on this iPad, but seems right. Someone should triple check all the calcs if the OP does want to do this in some fashion, I think we can sneak up on a real potential load.

Looks like Cobalt Carbonate price has dropped recently!
Petalite price hasn't...

Example of cobalt concentration vs depth of colour
Cone 6 Ultramarine Cobalt Blue Glaze (Glossy Clear plus Cobalt Carbonate)
https://www.thestudiomanager.com/posts/cone-6-ultramarine-cobalt-blue-glaze-glossy-clear-plus-cobalt-carbonate

Tst
... but it doesn't have the cyan-ish tinge.

Just another data point: electrical heating film for underfloor or sauna heating @ 440w/sq meter.  https://tinyurl.com/2abs2xdf
Didn't quite believe the difference in the wattage figures, so checked my maths.

The rather large difference maybe related to the speed of response required?

Thanks Peter - the 1% cobalt is close. Agree with you that a little more green needs to be added to get a blue closer to cyan. A good starting place though. May throw the question over to Glazy. Perhaps an Italian potter knows the formulation. I have Londi's bio, which I haven't read yet - may provide a few clues. Will report back if I nail it.