Buyers of stearic acid meet two naming systems at once: the old pressed classes (single, double and triple pressed) and numeric trade codes such as 1801, 1838 and 1842. Neither is a formal standard, and both are used loosely. This article explains where the names come from, what they usually indicate, how the grades compare, and how to read a specification so that you buy on numbers rather than labels. For a wider introduction, see our stearic acid guide.
Where the pressed names come from
Before modern hydrogenation, stearic acid was separated from mixed fatty acids by crystallisation and hydraulic pressing. The fatty acids were cast into cakes, wrapped in cloth and pressed to squeeze out the liquid oleic acid. One pressing gave single-pressed stearic acid, which still contained a fair amount of unsaturated acid. Pressing again gave double-pressed material, and a third pressing gave triple-pressed stearic acid, the purest and whitest of the three.
Today most stearic acid is made by fat splitting, hydrogenation and distillation, which remove unsaturation far more effectively than pressing. The pressed names survive as quality classes that describe how low the iodine value is and how good the colour is.
What the 1801, 1838 and 1842 codes usually mean
Numeric codes are producer and trade designations that became widespread with palm-based stearic acid. They are useful shorthand but not guarantees:
- 1801 is generally offered as a single-pressed or rubber grade, with wider limits on iodine value and colour.
- 1838 and 1842 are generally offered as higher-purity pressed grades. In many listings 1842 is described as triple pressed, while 1838 appears as either double or triple pressed, depending on the producer.
- For several 18xx codes, such as 1838, 1842 and 1865, the last two digits are often read as an approximate C18 content, so 1842 would contain roughly 42% stearic acid. The 1801 code does not follow that pattern.
Because different producers use the same code for slightly different products, always compare the full specification and recent certificates of analysis rather than the code alone.
Side-by-side comparison
The values below are indicative and vary by producer and feedstock. They are intended to show the pattern, not to replace a specification.
- Typical trade description: single pressed, often coded 1801, is a rubber or general industrial grade; double pressed is a general-purpose grade; triple pressed, often coded 1838 or 1842, is a high-purity grade for cosmetics, candles and plastics.
- Iodine value (g I2/100 g): single pressed is commonly specified up to around 8, although many current palm-based rubber grades are lower; double pressed is commonly up to around 4; triple pressed is typically 1 or below, often 0.5 maximum.
- Acid value (mg KOH/g): broadly 200–212 for all three, with tighter ranges on the purer grades.
- Titre (°C): roughly 52–57 for all three, depending mainly on the C16/C18 ratio.
- C18 content: less tightly controlled in single pressed; roughly 38–45% in common triple-pressed grades.
- Colour and heat stability: single pressed has the widest colour limits; triple pressed is near white with the best colour after heating.
- Typical uses: single pressed in rubber, PVC processing, metallic soaps and crayons; double pressed in candles, textiles, lubricants and general industry; triple pressed in cosmetics, white candles, light-coloured plastics and high-quality metallic stearates.
How to choose between them
Match the grade to the property that matters. Rubber compounds use stearic acid as an activator and processing aid, and small amounts of unsaturation rarely matter, so a single-pressed grade is often the economical choice; see our rubber and plastics page. Creams, lotions and white candles are sensitive to colour and odour over time, so a triple-pressed grade with a low iodine value is worth the premium; see our candles page.
Look at the C16/C18 ratio. Two triple-pressed grades with the same iodine value can crystallise differently if their C16/C18 ratios differ. In vanishing creams the ratio affects pearlescence and texture; in candles it affects crystal structure, hardness and surface finish.
Do not over-specify. A tighter grade costs more and may be harder to source. If your process tolerates a higher iodine value or a wider colour limit, specify that and keep the purer grade for products that need it.
Check consistency, not just the limits. Ask for several recent certificates of analysis. Lots that stay near the middle of the range are easier to process than lots that swing between the limits.
Reading a stearic acid specification sheet
A useful specification states each parameter with a unit, a limit and a test method. Check in particular:
- Acid value and saponification value, and the gap between them, which indicates unsplit glycerides or esters.
- Iodine value as a maximum, not a typical figure.
- Titre, with the method used.
- Colour, with the scale and cell size for Lovibond readings, or APHA units.
- Fatty acid composition by gas chromatography, including C16, C18 and minor acids.
- Moisture, ash and unsaponifiable matter.
- Physical form (beads, flakes or powder) and pack size.
Be careful with figures labelled typical: they describe an average, not a limit. For contract purposes, ask for guaranteed maximum and minimum values. To discuss a specification, see our palm stearic acid page.
Frequently asked questions
Is 1842 always triple pressed?
It is usually offered as a triple-pressed grade, but grade codes are not standardised. Check the iodine value, colour and composition on the specification rather than relying on the code.
Why is single-pressed stearic acid used in rubber?
In rubber, stearic acid mainly activates vulcanisation with zinc oxide and helps processing. A little residual unsaturation has little effect, so the lower-cost grade is usually adequate.
Does triple pressed mean pharmaceutical grade?
No. Triple pressed describes low iodine value and good colour. Pharmaceutical and food grades must meet the relevant monograph or regulation and need documentation for the specific product and site.
Can I replace one grade with another?
Sometimes, but test first. Differences in iodine value, colour and C16/C18 ratio can change cure behaviour, texture, colour stability or crystal structure in the finished product.
What does the iodine value tell me?
It measures the remaining unsaturated fatty acids. A lower iodine value means better colour and odour stability and more predictable behaviour on heating.