If you are buying borax in the UK, three documents tell you what you are actually getting: the label on the pack, the Safety Data Sheet (SDS) and the product specification. Real borax is sodium tetraborate, so a genuine pack should name the substance and its CAS number, carry the GB CLP health hazard pictogram with the signal word “Danger” and hazard statement H360FD, be marked “Restricted to professional users”, and come with an SDS. If those are missing, you are probably looking at a borax substitute or a poorly documented product. This checklist explains each item and how to compare grades before you order.
New to the chemistry? Start with our guide What Is Borax? Sodium Tetraborate Explained, then come back here for the buying side.
Step 1: Check the product identifier and CAS number
The word “borax” on its own does not tell you which compound is in the bag. The most reliable identifier is the CAS number, which should appear on the label, the SDS or the specification. The three commercial forms of sodium tetraborate differ only in their water of crystallisation:
| Label name | Formula | CAS number | Molar mass | B₂O₃ (theoretical) |
|---|---|---|---|---|
| Disodium tetraborate decahydrate (standard borax) | Na₂B₄O₇·10H₂O | 1303-96-4 | 381.37 g/mol | 36.5% |
| Disodium tetraborate pentahydrate | Na₂B₄O₇·5H₂O | 12179-04-3 | 291.29 g/mol | 47.8% |
| Disodium tetraborate, anhydrous | Na₂B₄O₇ | 1330-43-4 | 201.22 g/mol | 69.2% |
If a product calls itself “borax” but lists sodium carbonate (CAS 497-19-8) or sodium bicarbonate (CAS 144-55-8) instead, it is a borax substitute. That is not a fault: substitutes are made for household laundry and cleaning and contain no boron. Just make sure you know which one you are paying for. Boric acid (H₃BO₃, CAS 10043-35-3) is a different boron compound again and is not a like-for-like swap for borax.
Step 2: Read the CLP hazard label
In Great Britain, hazardous chemicals are classified and labelled under the GB CLP Regulation, which is enforced by the Health and Safety Executive (HSE). Sodium tetraborate in all three forms has a mandatory classification as toxic for reproduction, category 1B. On a properly labelled pack of borax you should see:
- Product identifier: the chemical name and CAS or EC number (for the decahydrate, EC 215-540-4).
- Hazard pictogram: the health hazard symbol (a figure with a starburst on the chest, known as GHS08) in a red-bordered diamond.
- Signal word: “Danger”. CLP uses “Danger” for the more severe hazard categories and “Warning” for less severe ones.
- Hazard statement: H360FD, “May damage fertility. May damage the unborn child.”
- Precautionary statements: typically including obtaining special instructions before use, wearing protective gloves and eye protection, and storing locked up. Suppliers choose the set, usually no more than six.
- Supplier details: the name, address and telephone number of the UK supplier, plus the nominal quantity in the pack.
Some suppliers also add an eye irritation statement (H319) based on their own assessment. Labels for hazardous products should not use reassuring words such as “safe”, “non-toxic” or “non-harmful”, so treat those words on a borax pack as a warning sign about the seller rather than about the chemical.
Step 3: Look for “Restricted to professional users”
Substances classified as toxic for reproduction, category 1A or 1B, fall under the restriction in entries 28 to 30 of Annex XVII to UK REACH. In short, they may not be supplied to the general public on their own or in mixtures at or above the relevant concentration limit, and suppliers must mark the packaging, visibly, legibly and indelibly, with the words “Restricted to professional users”.
That is why you will not find real borax next to the washing powder in a UK supermarket, and why specialist suppliers ask who the product is for. It remains lawful to buy and use borax for professional, trade, industrial and laboratory work. If you only need a laundry or cleaning aid at home, the right product is borax substitute, not borax.
Step 4: Get the Safety Data Sheet before or with your order
Under UK REACH, a supplier of a hazardous substance to a professional user must provide a Safety Data Sheet. A UK SDS follows a fixed 16-section format. When you are comparing borax suppliers, the sections that matter most are:
- Section 1: product name and supplier details, including an emergency telephone number.
- Section 2: the classification and label elements described above. These should match the pack.
- Section 3: composition, with the CAS number and purity.
- Section 7: handling and storage advice.
- Section 8: exposure controls and the personal protective equipment to use.
- Section 9: physical and chemical properties, such as pH and solubility.
- Section 13: disposal considerations.
Employers use the SDS to carry out the risk assessment required by the COSHH regulations, so a supplier who cannot provide one is not a suitable source for a workshop, studio or lab. We include an SDS with every order of borax decahydrate powder.
Step 5: Compare the specification, not just the price
Two white powders at the same price per kilogram can be very different products. A useful specification or certificate of analysis will show some or all of the following:
- Assay: the purity of the stated compound, for example 99.9% disodium tetraborate decahydrate.
- B₂O₃ and Na₂O content: these confirm which hydrate you have. A decahydrate should be close to 36.5% B₂O₃; a figure near 48% indicates pentahydrate.
- Impurities: limits for chloride, sulphate and iron, which matter for glazes, lab buffers, photographic developers and fine metalwork.
- Particle size: powder dissolves faster; granules flow better and make less dust.
- Batch or lot number: so a delivery can be traced back to its certificate.
Decahydrate vs pentahydrate: working out the real cost
Because the pentahydrate carries less water, each kilogram contains more borate. Dividing the molar masses (381.37 ÷ 291.29) shows that 1 kg of pentahydrate supplies the same amount of sodium tetraborate as about 1.31 kg of decahydrate. If a recipe, glaze formula or method specifies “borax” without a hydrate, it almost always means the decahydrate, so swapping in pentahydrate at the same weight gives you roughly 31% more borate than intended. Either check the formula’s assumption or adjust the weight.
For small benches, studios and labs, the decahydrate is usually the practical choice: it is the form most methods are written for and the one you will find in small packs. Our borax powder UK page compares the grades and pack sizes we stock.
Quick buyer’s checklist
| Check | What good looks like |
|---|---|
| Name and CAS | Disodium tetraborate with CAS 1303-96-4, 12179-04-3 or 1330-43-4 |
| Pictogram and signal word | GHS08 health hazard and “Danger” |
| Hazard statement | H360FD |
| Restriction wording | “Restricted to professional users” |
| Safety Data Sheet | 16-section UK SDS supplied before or with delivery |
| Specification | Assay, B₂O₃ content and batch number stated |
| Supplier | UK name, address and phone number on the label |
Safe handling and storage
Safety information. Borax (sodium tetraborate) is classified Repr. 1B, H360FD: may damage fertility, may damage the unborn child. For professional use only.
- Keep out of reach of children.
- Wear protective gloves and eye protection.
- Do not swallow. Never add borax to food, drink or cosmetics.
- Avoid breathing dust; work in a well-ventilated area.
- Do not use if you are pregnant or trying to conceive.
- Keep in the original, labelled packaging, sealed, dry and away from food.
- Read and follow the Safety Data Sheet.
Frequently asked questions
How can I tell if a product is real borax?
Check the CAS number. Real borax is disodium tetraborate, CAS 1303-96-4 (decahydrate), 12179-04-3 (pentahydrate) or 1330-43-4 (anhydrous), and its label carries the health hazard pictogram, the signal word “Danger” and H360FD.
Why does a borax label say “Restricted to professional users”?
Borax is classified as toxic for reproduction, category 1B. Under UK REACH, substances with that classification may not be supplied to the general public and their packaging must carry the words “Restricted to professional users”.
Should a borax supplier give me a Safety Data Sheet?
Yes. A supplier of a hazardous substance to a professional user must provide a Safety Data Sheet in the 16-section format. It is also what you need for your COSHH risk assessment.
Is borax pentahydrate stronger than borax decahydrate?
It contains less water, so it carries more borate per kilogram: about 47.8% B₂O₃ against 36.5% for the decahydrate. One kilogram of pentahydrate is roughly equal to 1.31 kg of decahydrate.
Does borax substitute have a hazard label?
Borax substitute is usually a blend of sodium carbonate and sodium bicarbonate with no boron. It is not classified as toxic for reproduction, but sodium carbonate is an eye irritant, so expect an eye irritation warning.
Sources
- HSE: The GB mandatory classification and labelling list (GB MCL)
- HSE: COSHH
- HSENI: CLP labelling and packaging
This guide is general information, not legal advice. Always follow the label and Safety Data Sheet supplied with your product.