How to write the appearance section of a Eucommia bark (Du Zhong) specification: raw vs salt-fried bark, surface colour, rubber threads, thickness and defect limits.
A specification line such as “dark brown, fibrous texture” sounds precise, but it can describe raw bark, salt-fried pieces, or a lot that was fried too long. Eucommia bark (Eucommiae Cortex, Du Zhong) is the dried stem bark of Eucommia ulmoides. Its visible traits carry both identity and processing information: surface colour, fracture behaviour, and the silvery rubber threads that appear when a piece is broken. A usable appearance specification names the form (raw or salt-fried), the outer and inner surface, the fracture, the cut size and thickness, and the visual defects that justify rejection. It also ties every statement to a reference sample. This guide shows procurement, QA, and OEM teams how to write each of those fields so that a supplier, an incoming-inspection team, and a customer’s auditor read the same document the same way.
A colour word is only an opinion until it is tied to a form, a surface, and a method of checking. Eucommia bark shows why. The outer and inner faces of one piece of raw bark are different colours, and processing changes the colour again. A buyer who writes “dark brown” and a supplier who ships raw bark with a pale outer face can both be acting in good faith, and the lot still ends up on hold.
Here is a short illustrative scenario (not a real customer case). A supplement plant orders “Du Zhong, dark brown, fibrous” for a decoction-style blend. The supplier ships raw, unfried bark. The plant’s QA team expected salt-fried pieces with brittle threads. Neither side broke any written rule, because the written rule did not say which form was meant.
There is also a conventional assumption worth qualifying: that the neater and more uniform the bark looks, the better the lot. Appearance tells you whether the material matches the expected identity and processing state. It does not tell you moisture, contaminant levels, or marker content. The ISO 8959:2024 standard for Eucommia ulmoides stem bark reflects this in its structure. Its published scope covers minimum requirements and test methods, and the contents of the final-draft text list macroscopic and microscopic characteristics next to moisture, ash, thin-layer chromatography, extractives, heavy metals, pesticide residues, and sulfur dioxide. Appearance is one layer of a specification, not a substitute for the others.
The most useful neutral reference is the macroscopic description in the final-draft text of ISO/FDIS 8959, the draft of the international standard for Eucommia ulmoides stem bark. In summary, it describes:
Three points about how to use this description.
First, it is a reference for raw material. The published standard states that it applies to whole medicinal materials and raw decoction pieces, and that it does not apply to processed decoction pieces. A salt-fried product needs its own appearance description (see below).
Second, the thickness range describes the bark piece itself. Cut length, width, and the thickness of cut pieces are separate fields.
Third, the text above comes from the final-draft preview. Buyers who copy figures into a contract should check them against the purchased, published edition of the standard or against the monograph of their target market.
Eucommia bark is traded raw and as a salt-processed product. A recent machine-learning study of Eucommiae Cortex processing degrees describes the key indicators of successful salt processing as a darker colour and lower elasticity of the gum silk. The same study separates four states: raw, under-processed, moderately processed, and over-processed. Those four states are the practical risk for a buyer. If the specification only says “salt-fried,” a lot can be anywhere on that scale.
Historically, the end point has been judged by eye and experience. A recent study on chromaticity and near-infrared analysis of salt-processed Eucommiae Cortex notes that processing degree had been judged by experience, which left quality of the finished decoction pieces hard to control. That is exactly the gap a written spec has to close.
| Spec element | Raw bark / raw decoction pieces | Salt-fried (processed) pieces | What to write in the spec |
|---|---|---|---|
| Reference description | ISO 8959 macroscopic description (final-draft text) | Not covered by ISO 8959; use the target-market monograph or the buyer’s own reference | Name the monograph, edition, and form |
| Surface colour | Pale brown to greyish-brown outside, dark purple inside | Darker than raw; pieces outside the agreed colour range may be under- or over-processed | Reference sample plus an agreed acceptable range |
| Rubber threads on breaking | Present as fine, dense, silvery, elastic threads | Elasticity reduced; threads break readily | A defined break test and a pass/fail reference sample |
| Main appearance risk | Wrong plant part, mould, unscraped coarse bark mismatch | Under-fried (too raw) or over-fried (too dark) pieces mixed in one lot | Maximum share of out-of-range pieces, agreed by count or weight |
| Typical verification | Visual, break test, identity test | Visual, break test, optional colorimeter reading | State method and sample size |
The study cited above measured powder colour (L*, a*, b*) with a spectrophotometer, so a colorimetric limit is technically workable. Whether it is necessary depends on how strict the downstream customer is. For most buyers, a signed reference sample with a stated tolerance and a photo record is the practical first step. Add L*a*b* limits only if a customer or a recurring dispute demands them, and set the range from the buyer’s own approved samples rather than from a generic figure.
A complete appearance section answers ten questions. Use the table as a template and delete fields that do not apply to the product format.
| Field | What to write | Why it matters | How it is checked |
|---|---|---|---|
| Botanical identity and plant part | Eucommia ulmoides Oliv., stem bark (not leaf) | The Chinese Pharmacopoeia lists bark and leaf as separate materials, so “Eucommia” alone is ambiguous | Documents, macroscopic and microscopic ID, TLC |
| Form and processing | Raw, or salt-fried, with the processing reference | Changes colour, threads, and decoction behaviour | Reference sample, supplier process record |
| Cut form and size | Pieces, strips, or slices, with a length and width range | Affects dust, packing, and extraction | Sieve or ruler on a defined sample |
| Thickness | Measured value, method, and acceptance rule | Prevents “too thick” arguments | Defined gauge, spot vs average, sample plan |
| Outer surface | Colour range, wrinkles or fissures, whether coarse bark is scraped | Distinguishes scraped from unscraped material | Visual against reference |
| Inner surface | Colour and smoothness | Part of the raw-material identity description | Visual against reference |
| Fracture | Presence and character of silvery rubber threads; break-test method | Identity and processing-state indicator | Break test against reference |
| Cleanliness | No live insects, mould, or visible foreign matter | The ISO draft requires clean, dry material with none of these present | Visual, odour, sieve |
| Fines and breakage | Maximum share of powder or fragments below an agreed size | Drives dusting, weight drift, and complaints | Sieve test |
| Reference photo and retained sample | Lot-matched photo set and sealed sample kept by both sides | Gives disputes an objective baseline | Document control |
The Chinese Pharmacopoeia point comes from a review of Eucommia ulmoides polysaccharides in Frontiers in Pharmacology, which notes that the 2020 edition includes the bark and the leaves as two distinct Chinese medicinal materials. In practice this means a spec and a COA should always state “bark” explicitly.
Appearance wording alone cannot settle thickness. A bark piece can be compressible, curled, or uneven, so two inspectors can measure the same piece and record different numbers. GuoCao’s guide on defining bark thickness by measurement method argues that a thickness figure should travel with the gauge, the foot size, the force, the dwell time, the sampling plan, and a stated acceptance rule. For Eucommia, decide whether you need spot thickness (relevant to cutter or filling-line jams) or average thickness (relevant to extraction consistency).
Cut form is a separate decision. Strips, blocks, and slices behave differently in decoction, tea-bag filling, and extraction, and the trade-offs are covered in choosing between bark slices, strips, or chunks. The cut form you choose also changes what “appearance” means: a strip is judged on width, length, and shedding, while a block is judged on size range and inner dryness.
The wording below is an illustrative template. Replace bracketed items with figures from your own pharmacopoeia, customer requirement, or approved reference sample.
Raw bark: Eucommia ulmoides Oliv. stem bark, dried. Flat or slightly inward-curved pieces. Outer surface pale brown to greyish-brown, wrinkled or fissured, [scraped / unscraped]. Inner surface dark purple, smooth. Fracture shows fine, silvery, elastic threads when broken by [defined method]. Free of live insects, mould, and visible foreign matter. Thickness measured by [gauge, foot size, force, dwell time], [target range], [acceptance rule]. Fines below [mesh/size]: not more than [X]%.
Salt-fried pieces: As above, processed with salt solution by [stir-frying method]. Colour within the approved reference range; threads reduced in elasticity and break readily. Under-processed and over-processed pieces: not more than [X]% by [count/weight]. Reference sample No. [ ] and lot photo set attached.
Two practical details strengthen the clause. Take reference photographs on a neutral background, under consistent lighting, and with a scale visible, and keep a sealed retained sample from the same lot. And for incoming inspection, open cartons across the lot rather than the most convenient two or three. The sampling logic in GuoCao’s bulk sourcing guide for bark Chinese medicinal materials is useful here, including its recommendation to request a pre-shipment sample from the same lot.
The same bark does not need the same visual specification in every channel. For decoction pieces, recognisable morphology and clean cut form matter most because practitioners and pharmacists inspect the pieces. For tea bags, fines and dust control matter because they cause weight drift and sealing problems. For extraction or milling feedstock, visual neatness matters less than identity testing and consistent processing state. For readers mapping those channels, GuoCao’s overview of how Du Zhong is used in decoction slices, tea bags, and supplement formats is a useful companion. That overview covers appearance only briefly, so use a pharmacopoeial or ISO description as the technical reference when drafting the appearance section.
Appearance fields also have to sit inside the wider document. A factory’s incoming-quality team will check the appearance statement against the COA, the label, and the lot code. The structure for that wider document is set out in GuoCao’s guide to creating a specification sheet for Chinese herbal slices for pharma and supplement factories, which separates identity, physical, chemical, contaminant, microbial, traceability, and storage sections.
Send these items with the RFQ so the supplier can quote the right material and the first sample is comparable:
Buyers who want to see what is currently offered can start from the Eucommia bark (Du Zhong) bulk supply page. Treat the one-line appearance and form fields on any product page as a starting point, then ask the supplier to confirm each field in your own specification, with a lot-matched sample and COA, before the first order.
State the form (raw or salt-fried), outer surface colour and texture, inner surface colour, fracture behaviour with silvery rubber threads, cut size, measured thickness, and defect limits. Attach a reference sample or photo set and name the pharmacopoeia or standard used.
The ISO 8959 final-draft description gives flat or slightly inward-curved pieces, 0.3–0.7 cm thick, with a pale brown to greyish-brown wrinkled outer surface, a smooth dark purple inner surface, and fine silvery elastic threads at the fracture.
No. Threads are a strong visual indicator, but other rubber-containing plants can also produce threads. Combine the break test with documented identity testing, such as macroscopic and microscopic identification or TLC, and with plant-part and origin records.
No. Its scope covers whole medicinal materials and raw decoction pieces and excludes processed decoction pieces. For salt-fried pieces, specify the target-market monograph or your own approved reference, and define colour and thread brittleness.
Salt-fried pieces are darker and the gum silk is less elastic than in raw bark. Pieces outside the agreed colour and brittleness range may be under- or over-processed, so the spec should include a reference sample and an agreed share of out-of-range pieces.
Not on its own. Raw bark has a pale outer face and a dark purple inner face, and processing darkens the colour further. Write colour by surface and form, and anchor it to a signed reference sample.
No. Appearance checks identity, processing state, and cleanliness. Moisture, ash, chemical identification, contaminants, and microbiology need separate tests, which is why a COA should list methods and acceptance criteria next to the visual statement.
