Babs

You could coat your ware with a white slip if yoy cant get a white body

Barium carbonate will only precipitate out soluble salts not the iron etc. impurities.  I would try every clay you can buy and see which one works the best.

You could coat your ware with a white slip if yoy cant get a white body

Similar look with Jeffrey Nichol's work, multiple layers of underglaze applied on top of the clay then sanded through.

First guess is two or more layers of different colored slips/underglazes on textured porcelain, then scraped, followed by sanding after bisque to really clean it up. Whatever she’s doing it’s marvelous. 

Yes , folk get that haloed effect when carving layered coloured slips in the sgraffitti technique.

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
 
 

If the bottom is particularly thin that may also have some bearing on the problem. Again to reference Hamer and Hamer’s book, the section on crack diagnosis is outstanding. 

To me it looks as if glazes or slip are layered onto a textured piece and then partially removed by sanding or other method then fired. Almost looks like "raindrop damascus " in a way.

Could always take a clear which contains either Lithium, petalite or Barium Carb and test tile them with varying abmounts of Copper Carb.  What cone are you firing to?
Ceramic Arts had a Wrights water blue of similar colour in its free midfire glaze download at one point. If you have a buff or dark clay body you can coat with a white slip to get the bright colour.
 

Hamer suggests the gaze layer inside isthick, even thicker than base of pot.
Smash the pot to see if the turned base is thinner tgan rest of pot.
Body contracts more than glaze and so cracks.
Maybe wipe pots with indian ink when come out of kiln,may show the crack actually exists then,or it can happen later. 

It reminds me of a glaze known as “water blue” that uses copper carb. Some versions have strontium and lithium, some don’t. 

What Kelly is referencing is available to see in a Google book preview here. Have a look at crack "F". Highly recommend this book!
https://books.google.ca/books?id=TApnGTVLwxAC&pg=PA86&lpg=PA86&dq=hamer+and+hamer+cracks&source=bl&ots=inS6KQPb4N&sig=ACfU3U3-WW9HznLwIEytHMyGanL2bpymZA&hl=en&sa=X&ved=2ahUKEwiG1JCB0KPgAhWyPH0KHX7EBo4Q6AEwB3oECAcQAQ#v=onepage&q=hamer and hamer cracks&f=false

Hamer suggests the gaze layer inside isthick, even thicker than base of pot.
Smash the pot to see if the turned base is thinner tgan rest of pot.
Body contracts more than glaze and so cracks.
Maybe wipe pots with indian ink when come out of kiln,may show the crack actually exists then,or it can happen later. 

Hamer suggests the gaze layer inside isthick, even thicker than base of pot.
Smash the pot to see if the turned base is thinner tgan rest of pot.
Body contracts more than glaze and so cracks.
Maybe wipe pots with indian ink when come out of kiln,may show the crack actually exists then,or it can happen later. 

Hamer suggests the gaze layer inside isthick, even thicker than base of pot.
Smash the pot to see if the turned base is thinner tgan rest of pot.
Body contracts more than glaze and so cracks.
Maybe wipe pots with indian ink when come out of kiln,may show the crack actually exists then,or it can happen later. 

Think the blue is from Copper Carbonate, maybe a smidgeon of Cobalt,  just my opinion.

Research majolica glazes and Linda Arbuckle, she is the best.

Think the blue is from Copper Carbonate, maybe a smidgeon of Cobalt,  just my opinion.

Research majolica glazes and Linda Arbuckle, she is the best.

Oh now I have to choose mentally, ( my son gave me a gift voucher for $150 ) and with Pres's I would have 300!!! 
Prob only $150 of Callie'sCanadian 
Power drill of my own, mmm, delicious
New worktable...., well just think I need proper tool organisers and brush holder.
Put $ towards slab roller.....
Prob. My indecision shows nothing screaming at me.
 

So $150 US is closer to $180 CAD, so i got a little more to work with (evil smile!)
The first thing that jumped to mind was more mason stains, or tracking down some rare earth minerals for colourants. I don’t own a digital scale, and that’s on my list of nice to have things. But like a lot of folks, I already have a bunch of stuff, and most of my go-to tools are really cheap ones. 
The things that have been a worthwhile $150 bucks included proper shelving and a glaze screen that fits over a bucket nicely. And a good corded drill capable of mixing grout. The piece I was kind of surprised to use as much as I do was a good banding wheel. I inherited mine, but a new one is in that range, so worth a mention. 

I tend to prefer simple and inexpensive tools. If I was being forced to spend $150, I would spend it all on various ribs. Different sizes, shapes, and materials. 
The one expensive tool that I would buy again in a heartbeat is the Giffin Grip. 

oooooo.....you pushed my "back in the day" larceny button (gone, but not forgotten)! I'd take the $150, tell you I bought such & such, and go spend a night at the beach off season. Actually, since I indulged myself when I set up my studio, I have all the tools I need & then some.