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Winter can make routine embedding and sectioning significantly more difficult. Even small drops in room temperature or humidity can alter the way paraffin solidifies, how tissues respond to mechanical stress, and how smoothly microtome components operate. Paraffin contracts more sharply in cooler air, tissue becomes mechanically less predictable, and lubricants on equipment can thicken or behave inconsistently. In addition, cassettes that move between different temperature zones—such as from a cold grossing area into a warm processor—can experience sudden thermal gradients that disrupt infiltration. These subtle but cumulative environmental effects often appear as chatter, brittle ribbons, thick–thin artifacts, or infiltration irregularities that don’t show up during warmer months. Below are the key mechanisms and practical fixes based on current protocols and materials literature.
Paraffin becomes firmer and is more prone to cracking as it cools
When molten paraffin cools, it solidifies and contracts. In colder ambient air, this cooling happens faster, and blocks can develop internal stresses or small splits at the tissue-wax interface. The result can be chatter, difficulty getting continuous ribbons, or fragile fragments from delicate tissues. Practical fixes: let blocks warm and equilibrate 5–10 minutes before sectioning, keep blocks away from drafty or unheated areas, and consider raising your embedding center temperature 1–2 °C during cold months. 1,2
Tissue mechanical properties change with temperature
Fatty tissue tends to firm up and appear glassy in cold conditions, while some soft tissues can become brittle and tear more easily. These biomechanical changes increase the likelihood of tearing or fragmentation during microtomy. Practical fixes: briefly hydrate or humidify blocks before initial facing, and take slower, slightly thicker initial passes to let the block and blade equalize. 3,4
Microtome components and lubricants are temperature-sensitive
Cold reduces lubricant fluidity and can change clearances in bearings and moving parts, making handwheels feel stiff or inconsistent. This affects the smoothness of the cutting stroke and can cause thick–thin artifacts. Practical fixes: allow instruments to reach operating room temperature before heavy sectioning, and check lubrication/maintenance schedules more often in winter. 5,6
Processing and infiltration can be less predictable if cassettes are cold
If cassettes are placed into processors or molten paraffin before they’ve equilibrated from a cold grossing area, paraffin viscosity and thermal gradients can cause uneven infiltration and occasional soft cores. Practical fixes: let cassettes warm to room temperature before embedding or increase infiltration dwell times by a modest amount (e.g., 15–20 minutes for very dense samples) when needed. 3,4
Winter introduces subtle but meaningful challenges in microtomy and embedding, many of which stem from temperature driven changes in paraffin behavior, tissue consistency, and equipment performance. By anticipating these seasonal shifts—warming blocks, monitoring humidity, adjusting equipment temperatures, and ensuring instruments and reagents are properly acclimated—histology teams can significantly reduce artifacts and maintain consistent section quality. With a few small workflow adjustments, even the coldest months can run smoothly at the microtome.
Written by: Antoinette EF Lona, MSc., HTL(ASCP)CM
References
- Silva-Nava V, Hernández-Pérez JA, Flores J, et al. Thermophysical characterization of paraffin wax. MDPI. Published online [year unknown]. Accessed November 30, 2025.
- CELLINK. Paraffin embedding protocol. CELLINK protocol resources. Accessed November 30, 2025.
- StainsFile. Paraffin processing and infiltration theory. StainsFile Histology Reference. Accessed November 30, 2025.
- Corning. Technical note: Processing and infiltration recommendations for dense tissue. Corning Life Sciences. Accessed November 30, 2025.
- SKF. Low-temperature effects on lubricants and bearings. Evolution—Technology Magazine from SKF. Accessed November 30, 2025.
- Carson FL, Cappellano CH. Histotechnology: A Self-Instructional Text. 4th ed. American Society for Clinical Pathology Press; 2015.
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