A charcoal clamp (mielerz) is a pile of wood covered with an earth cover; a retort is a steel chamber with a lid. In both, wood turns into charcoal with restricted access to air. Choose a phase in each cross-section separately: the drawing, the description of the work and the state of the wood will change, and copper will mark the layer that matters in that phase.
Earth charcoal clamp5 phases, cover built anew
Our own illustrative diagram of a cross-section of the pile, not to scale. It does not document any particular charcoal clamp.
Phase
Phase 1 of 5Stacking around the central channel
Action
Split logs are stood around a vertical channel, the średzina, so that the stack takes the shape of a dome.
State of the wood
Raw, with water in it.
Layer
The charge and the central channel. There is no cover yet.
Basis
The description of the stack and the term “średzina” come from the V2 notes (E. Marszałek, 2013). They were not checked again.
Phase 2 of 5Covering with the earth cover
Action
The stack is covered with a layer of plant material and earth, the cover (opona). It is meant to restrict the supply of air so that the wood chars rather than burns.
State of the wood
Raw, not yet lit.
Layer
The covering, that is the cover.
Basis
The function of the cover according to the V2 notes. Composition and thickness of the cover in the Bieszczady: not established in this material.
Phase 3 of 5Lighting and managing the burn
Action
The charcoal burner watches the stack and regulates the draught through holes in the cover. First water escapes from the wood, then its components break down and release gases.
State of the wood
Charring in progress. The drawing shows this schematically as a growing core of charcoal.
Layer
Draught channels: the central channel and the holes.
Basis
The actions (e.g. piercing holes with a rod) come from the V2 notes. Time and temperature depend on the equipment and the charge. They are not in the material, so we do not give them.
Phase 4 of 5Sealing and cooling
Action
As the burn nears its end, the holes are plugged with wet earth. The clamp cools without access to air, so the charcoal does not turn to ash.
State of the wood
Charcoal, still hot.
Layer
The covering and its tightness.
Basis
V2 notes. The order of events in a particular burn has not been confirmed here.
Phase 5 of 5Removing the cover and drawing the charcoal
Action
Only after cooling is the cover taken apart and the charcoal drawn out, sieved and packed.
State of the wood
Finished charcoal: porous, light, with a trace of growth rings.
Layer
The charge.
Basis
V2 notes. The description of the charcoal structure matches the drawing at the top of the page.
Steel retort5 phases, casing stays
A general illustrative diagram, not to scale. The arrangement of openings of the “Las” kiln is not reproduced here: there is no drawing in the material.
Phase
Phase 1 of 5Loading
Action
Wood goes into the steel chamber with the lid off.
State of the wood
Raw, with water in it.
Layer
The charge.
Basis
V2 notes. The drawing is general and does not reproduce the “Las” kiln.
Phase 2 of 5Closing the lid and lighting
Action
The lid closes the chamber. Air is restricted by the steel casing, not by an earth cover that would have to be built anew. The charcoal burner lights the charge.
State of the wood
Raw, water begins to evaporate.
Layer
The covering: casing with a lid.
Basis
According to the V2 notes, the casing and lid replaced the earth covering of a charcoal clamp. How a particular retort was sealed: to be established.
Phase 3 of 5Burning through the chimneys
Action
The charcoal burner regulates the flow of air and gases through the openings and chimneys in the casing.
State of the wood
Charring in progress.
Layer
Draught channels: the lower air inlet and the chimneys.
Basis
V2 notes. The number and position of openings in the “Las” kiln: there is no drawing in the material. Time and temperature depend on the equipment and the charge, so we do not give them.
Phase 4 of 5Cutting off air and cooling
Action
The air inlet and chimneys are closed, and the charge cools in the closed chamber.
State of the wood
Charcoal, cooling.
Layer
Draught channels, this time closed.
Basis
V2 notes. Its claim that steel cools faster than the earth cover we leave out as unverified.
Phase 5 of 5Unloading, casing stays
Action
After cooling the lid is taken off and the charcoal is drawn out. The casing waits for the next charge; nothing is taken apart.
State of the wood
Finished charcoal.
Layer
The charge.
Basis
V2 notes and the description of the SGGW retorts from 1980 (E. Marszałek, 2013). To be checked in the study.
How they differ (content from the V2 notes, to be checked against the sources)
Layer
Charcoal clamp
Retort
Covering
Cover of plant material and earth, built for every burn.
Steel casing with a lid, reused.
Draught
Central channel and holes pierced in the cover, regulated during the burn.
Air inlet and chimneys in the casing; the layout of a particular kiln is not reproduced.
After the burn
The cover is taken apart, the charcoal drawn out.
The lid is taken off, the casing waits for the next charge.
The phases are not paired one to one. The charcoal clamp has a stage the retort does not (building the cover), and the retort ends with unloading a device that stays. Only the sequence of the wood’s state is shared: raw, charring, charcoal.
raw wood
charring in progress
charcoal
cover / casing
the layer that matters in this phase
arrows: solid are air, dashed are gases (diagram)
Explanation · a model, not a measurement
How much of the charge ends up as charcoal
For the same volume of wood, moisture changes the mass that is loaded and the amount of water to be evaporated. In this model it does not change the amount of charcoal. The yields are assumptions you can move, because for the Bieszczady we do not know them.
Charcoal clamp
Retort
0400 kg800 kg
Common scale: the full width is 800 kg, that is 1 stacked m³ at the highest moisture on the slider. Tick marks every 100 kg.
Mass per 1 stacked m³ of charge, kg
Component
Charcoal clamp
Retort
Water evaporated
133 kg
133 kg
Gases and volatile vapours
320 kg
280 kg
Charcoal
80 kg
120 kg
Total (wet charge)
533 kg
533 kg
Wet charge per 1 kg of charcoal: charcoal clamp 6.7 kg, retort 4.4 kg.
Model: dry mass of wood 400 kg per stacked m³ (hypothetical). Charcoal = yield × dry mass. Gases and vapours = dry mass − charcoal. Water = wet mass − dry mass. The model does not count air or ash and does not describe any particular burn. For n stacked m³ multiply the results by n.
Documented work
What is known about this work, and what is missing
The dry distillation of wood can be discussed in general terms. About the actual work in the Bieszczady this material says little: it points to three dates from a study and from information published by the State Forests (Lasy Państwowe).
The charcoal burner’s voice
Here would stand one sentence from a person who did this work. The space is empty.
Note: the input materials contain no statement and no consent to publish one. We do not invent a quotation.
Documented points (according to the V2 notes)
1980At SGGW (Warsaw University of Life Sciences) a technology of steel retorts was developed for the “Las” enterprise. This is the date of that technology, not of the first retort in the world.
2013E. Marszałek’s study on saving the charcoal-burning profession: stages of the work, terminology (średzina, opona), the replacement of charcoal clamps by retorts.
2016The State Forests describe an open-air exhibition by the Stuposiany–Muczne road: a model of a charcoal clamp, retorts and a charcoal burners’ hut.
What is not here
The duration or temperature of a particular burn. They depend on the equipment and the charge, which is why the cross-sections have no time axis.
Drawings and photographs of a single documented retort, or museum material on the charcoal clamp.
A pair of wood and charcoal samples with a scale. The drawing at the top is a diagram.
Measurements from the Bieszczady of yield, density and moisture of wood.
The photograph of retorts by the road to Łopienka of 15 August 2016 (Michal Derela, Wikimedia Commons, CC BY-SA 4.0) is only a link in the sources. We do not embed it so that the page works offline. The author and licence come from V2 and were not checked now.
Caution
Traces in the forest: questions instead of identification
The shape of the ground alone does not show that a charcoal clamp or a retort stood in a given place. Four features you may notice, and what else they may mean.
A circular or oval outline of a levelled patch
It may also be a skidding terrace, a timber landing, a natural level patch or a hollow left by an uprooted tree.
Specks of charcoal on the surface
They may come from another fire. Their absence settles nothing either.
Steel elements, slag, a hardened access track
They may be linked to later forestry. Their presence alone does not prove a retort.
Closeness to a stream
The V2 notes linked it to the need for water. It is a hint about context, not proof.
From the surface one can usually say only: a possible trace, not identified.
Do not dig, do not strip the forest litter and do not use a metal detector without the consent of the forest manager and the heritage conservation authorities. The V2 notes state that this is prohibited; the regulations were not checked here.
Do not publish exact coordinates. Describe the place in general terms or report it to the forest district or the conservator.
This page does not identify sites and does not replace the decision of the land manager.
Explanation and limits
What this page is, and what it is not
Status of the material
The drawings (the discs at the top, the cross-sections) are our own illustrative diagrams, not to scale. They are not photographs, maps or documentation of equipment.
The descriptions of the phases and the terminology come from the V2 notes. The source links were kept, but in this version they were not opened or checked again.
The mass balance is a teaching model with explicit assumptions.
This is a working version V3; it has not passed a substantive review or acceptance.
Missing materials
A pair of wood and charcoal samples with a scale.
Photographs or drawings of a single documented retort.
Museum material on the charcoal clamp.
A statement from a charcoal burner together with consent to publish.
What changed compared with V2
Three layer toggles were replaced by highlighting one layer in each phase. The toggles allowed states that do not exist (e.g. a stack without a cover during the burn).
The temperature table and smoke colours were removed: the material contains no values for a particular burn.
The volume slider and “10 kg sacks” were removed: linear scaling that explains nothing. The result is per 1 stacked m³.
The choice of “variant A or B only” was replaced by showing both models at once.
The sheet of sites A–D with a “diagnosis” was removed. It was replaced by questions and the rule “not identified”.
The photograph of retorts became a link, not an embedded image.
Kept: the course of the burn for both technologies (with a different division into phases), the yield × dry mass relationship, the definition of moisture as the share of water in the wet mass, four sources and the rules for protecting the landscape.