Ultramarine Blue

Overview

Ultramarine blue is a synthetic mineral pigment — a complex sodium aluminum sulfosilicate — that produces a rich, vivid blue with a slightly violet undertone. Historically, natural ultramarine was ground from lapis lazuli and was more expensive than gold. The synthetic version, developed in the 1820s, is chemically identical, far purer, and affordable enough to put in bath bombs.

Cosmetic-grade ultramarine blue is widely used in eyeshadow, soap, bath products, and decorative cosmetics wherever you need a true blue. It is also available in violet and pink variants (different heating and processing conditions shift the hue), though the classic blue is by far the most popular.

The pigment is very lightfast and heat-stable, which makes it reliable in most formulations. However, it has one critical limitation: ultramarine blue is not stable below approximately pH 3. In acidic conditions, the sulfur bonds in the crystal lattice break down, the pigment loses its blue color and turns grey-brown, and it releases hydrogen sulfide (which smells like rotten eggs). This means you cannot use it in AHA serums, acidic toners, vitamin C formulas, or any product with a low pH.

What it does in a formula

Ultramarine blue provides opaque-to-semi-opaque blue color. It is the go-to pigment when you need a clean blue that does not bleed, does not migrate, and holds up to heat processing. In eyeshadow, it delivers rich cobalt-to-navy tones depending on concentration. In soap, it produces vivid blue swirls. In bath bombs, it colors water a striking blue without staining the tub.

The violet and pink variants extend the range — ultramarine violet gives a cool purple, and ultramarine pink delivers a muted mauve-pink that works well in blush formulas.

How to use

Pre-disperse in a small amount of oil (for anhydrous products) or glycerin (for water-based products) before adding to the main batch. Like all mineral pigments, dry powder will clump if added directly.

Usage rates by product type:

• Eyeshadow: 2-5% (blended with mica or sericite base)
• Cold-process soap: 0.5-1.5% (per pound of oils)
• Bath bombs: 0.5-2%
• Lip products: 0.5-2% (check local regulations — some jurisdictions restrict ultramarine in lip products)
• Loose powder cosmetics: 1-5%
• Melt-and-pour soap: 0.25-1%

No special temperature requirements — ultramarine is heat-stable well beyond normal cosmetic processing temperatures.

Best for / Worst for

Best for: eyeshadow, pressed powder cosmetics, cold-process soap, bath bombs, bath salts, melt-and-pour soap, color cosmetics needing a true blue, any product at pH 5 or above.

Worst for: any product below pH 3 (AHA peels, low-pH vitamin C serums, acidic toners), products where you need a transparent tint rather than opaque color, formulas that might shift to low pH over their shelf life.

Common pitfalls

Using in acidic formulas. Below pH 3, ultramarine blue degrades — it turns grey and releases hydrogen sulfide gas. Check the pH of your finished product. Anything above pH 4-5 is safe.

Assuming all “blue pigment” is interchangeable. Ultramarine blue, phthalo blue, and various blue lakes have completely different chemistries and regulatory statuses. Do not substitute without checking.

Poor dispersion causing streaks. Mineral pigments need mechanical dispersion. Stir harder or pre-grind in a mortar before adding.

Regulatory confusion on lip use. In the US (FDA), ultramarine blue is approved for external cosmetics including the eye area but is NOT approved for lips. In the EU, it is permitted in lip products. Check your local regulations before formulating.

Overdoing it in soap. Ultramarine blue is potent — 0.5% gives a medium blue in cold-process soap. Going above 1.5% often results in pigment that washes out of the bar and onto washcloths.

Substitutes

• Indigo powder (natural) — plant-derived blue, but less vivid and less stable. Shifts green in some formulas.
• Blue mica blends — pearlescent blue rather than opaque, good for shimmer eyeshadow.
• Phthalo blue (CI 74160) — synthetic organic pigment, very vivid blue, different regulatory profile.
• Woad powder — historical plant blue, similar to indigo, very muted.
• Blue spirulina extract — water-soluble natural blue, not stable in most formulas, better for short-shelf-life products.