The most useful thing I can tell you before anything else: when mixing two clay bodies for marbling, stay within the same supplier. A Standard stoneware with a Standard porcelain. A Montesa body with another Montesa body. Not a Standard porcelain with a SIO-2 stoneware. This sounds simple, but it took me a number of failed batches to commit to it as a rule rather than a suggestion.
Each manufacturer formulates differently. Even when two clays share the same cone range, their plasticity, shrinkage rate, and behavior when wet can differ significantly. When you're marbling, those differences get amplified. What's a small inconsistency in a single clay becomes a visible problem across two. Seams appear. The twist breaks down. The slab doesn't move as one piece.
Everything below is a record of what I've tested, organized by supplier and combination. Cone 6 throughout.
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Standard Ceramics
308 Brooklyn Red + 365 Grolleg Porcelain
The red body fires to a deep, iron-rich tone. Against the porcelain, the contrast is strong but warm. Again tested both ways. The unglazed version has a rawness that reads well on larger forms.
365 Porcelain + stain
Technically this is one clay body with a stain mixed into part of it rather than two separate bodies. It's the cleanest combination I've worked with, because there's no clay body tension at all. The base is identical. The blue reads saturated and even under clear glaze. If you're new to marbling and want a predictable result, start here.
112 Brown + 365 Grolleg Porcelain
Both Standard, both cone 6. A reliable combination. The warm brown body and the white porcelain move together well. The contrast is earthy rather than graphic. I tested with and without clear glaze. The glazed version shows the marbling pattern more clearly. The unglazed version has a dry, sandy quality that I prefer for decorative work.
Montesa + Vicente Diez
Porcelain Vicente Diez + Black Stoneware
Within supplier, cone 6. High contrast. The colored porcelain and dark body work against each other graphically. The glazed surface deepens and enriches the pattern.
Pasta Negra + Tostada + Moteada
All Montesa, all cone 6. A three-body combination. The result is more geological than graphic. The tones are close enough that the marbling reads as strata rather than contrast. Quieter, but intentional.
SIO-2
This supplier requires its own section because the clays behave differently from Standard or Montesa. The plasticity is genuinely distinct. Not worse, just different in a way that matters when you're combining with another manufacturer's body. Here comes my first mistake.
PRNI Black Stoneware + 365 Porcelain (Standard) — avoid
This is the cross-supplier combination I'd steer you away from. The plasticity difference between the SIO-2 black and the Standard porcelain made the marbling process difficult to control. The clay bodies don't want to move together. The results weren't worth the trouble. Some areas even start to peel and there are visible cracks. I've marked this one as AVOID.
182 Angel White + PRNI Black Stoneware
I have a big batch of PRNI Black Stoneware and I don't want to loose it. The best white match from Standard is 182 Angel White. These work. The Angel White's plasticity is close enough to the PRNI black that the marbling process felt cooperative. No forced seams, no breakdown in the twist. The contrast is quieter than a stark white porcelain against the black, which I think suits the SIO-2 surface quality. A combination worth repeating.
The black stoneware problem
Black stoneware does not stay black under a clear glaze. What you get is brown. A warm, toasty brown that isn't unpleasant, but it is not what you see in the raw clay. The iron and manganese that give the body its dark color react differently in the kiln when covered by a transparent glaze.
Unglazed, it's a different result. The matte dark surface has a depth and complexity that the glaze actually obscures. For purely decorative work, leaving it unglazed is often the better choice. If the piece needs to hold food or liquid, glaze the interior and decide how you feel about the color shift on the exterior. Or accept the brown and work with it. It can be beautiful. It's just not the same thing.
The pattern is consistent: same supplier, both bodies. SIO-2 works well within itself. Crossing suppliers is where problems start. For the data behind the groupings, the clay body compatibility guide has the full chart. For stain percentages and mixing notes, the How to Add Color to Clay guide covers cone 6 results across common clay bodies.
More combinations in progress.
