GemLab LED microscope - maxxiLED-2
Treatment   Untreated-treated rubies-sapphires for study, reference and research
  "The Heat Treatment of
Alchemy & Science"
by Ted Themelis
Articles   Read below interesting topics on gem treatments

Heat treatment technology
Heat treating ruby-sapphire
Beryllium detection with LIBS
Lead-filled rubies
Cranking up the heat
Treatment disclosure

A REMINDER "Forty years ago, I used to sell Ted's first microscope and other accessories. Before his death, R.T. Liddicoate saId Ted Themelis was one of the three individuals whose ideas pose the greatest threat to the GIA."" Dr.W.Hanneman

Gemlab Mini Muffle Furnace (Model M50P-1700)

Gemlab's M50P-1700 ("MINI MUFFLE") vertical muffle, bottom-loaded furnace is designed by Ted Themelis in response to the market demand for mini-size, desk-top, high temperature reliable furnace. Model M50P-1700 is the smallest possible vertical muffle furnace can be engineered which rubies-sapphires can be easily loaded-unloaded into/from the heating chamber via a manually operated mechanical elevator. The furnace is able to heat-treat one crucible filled with 1,140 cts of rubies-sapphires at any temperature to 1700oC in air, reducing, oxidizing or in vacuum, with or without additives as desired by the user. The furnace may be used without muffle to increase loading capacity.

Model M50P-1700
Immediate delivery, FOB Bangkok

Model M50P-1700 Features & specifications
Bench-top, only 400 (D) x 400 (W) x 980 (H) mm
Net weight is only 95 kgs
Max. operating temperature is 1700oC; 1720oC with 1850-grade heating elements (special order)
Loading capacity: maximum 1,140 cts of corundum
Double steel shell design with dual cooling air fans
Full atmosphere control module for reducing-oxidizing
Vacuum pump withsolenoid valve and vacuum gauge
Molybdenum desilicide 1800-grade elements
Auto tune, 51-step, artificial intelligent temperature programmer/controller with highl accuracy and easy operation
Eurotherm SCR (Silicon Control Rectifier)
Long life Pt/Rh “B” type thermocouple (1 set)
Highest energy fiber-board 1900-grade hot-face insulation
Voltmeter, ammeter, on-off switch, alarm-buzzer, key-switch

Mechanical elevator for manual loading-unloading

Power: 1.8 KVA, plugs to any 220 Vac 10 A (1 phase)
Very low electric power consumption
Safe and easy operation
Long-lasting performance
One year warranty on all electric, electronic parts

Modes of loading and capacities (Model M50P-1700)
  FURNACE CONFIGURATION. The heating process of the stones is performed using an alumina (99.96% purity) muffle tube, COE (Close-One-End), OD=50 mm, L=280mm mm, fastened hermetically and securely with metal flange assembly. In this mode, selected gases generated in the atmosphere control module can be purged directly to the muffle in "open-loop" mode, thus providing controllable atmosphere conditions with positive pressure up to maximum 1800oC temperature, or in vacuum -up to maximum 1500oC. The crucible is loaded in the chambers from the bottom using mechanical elevator and supported by special reticulated alumina post.
  SELECTIVE LOADING (6 DISHES). The unique feature of the M50P-1700 is the ability to load small quantities of ruby-sapphire in 6 alumina (99.6% purity) dishes which are inserted into the crucible and then in the muffle. Each dish is OD=30 mm, H=16 mm (each dish 83 cts, total 498 cts); the 6 dishes fit into one crucible OD=40mm H=100 mm. In this mode, stones from different localities, or stones with different features may be grouped and heated together on the same time, under the exact heating parameters without been mixed or contaminated each other. Likewise, fluxed and unfluxed stones may be placed in different dishes. Loading these stones in this method is particularly useful in research heating projects where contamination must be avoided and precision is required.
  BATCH LOADING FOR BULK PROCESS. To obtain maxium load capacity (1,140 cts) rubies-sapphires may be loaded in one crucible and inserted into the ceramic muffle tube. This mode is suitable for heating corundum in the bulk with or without using additives under any atmosphere..
Glipses and Feature of Model M50P-1700
Model M50P-1700 can reach 1700oC without the use of water cooling re-circulation to keep the muffle flanges below 90oC ; though this mode is satisfactory and workable for relatively short soaking periods of time (hours), water cooling system (optional) is desired when wrorking above temperatures above 1300oC and prolong soaking periods (weeks, months). The metal flange assembly is already equipped with water inlet-outlet fittings to connect hoses form the water cooling module; the cooling module is optional.
Control console of model M50P-1700 shows PV (Process Value) and SV (Set Value) in complete agreement at 1700oC; Pilot light shows the furnace is in RUN mode, LED bar indicator of the temperature- programmer/controller is about 65% ( still 35% power available). Output voltage is 14 Vac and Current about 60 Amps, thus the power is about 840 Watts.
Standard Equipment for M50P-1700

Heating elements. One set (3 ps) of 1800-grade MoSi2 heating elements. Maximum element temperature in air is 1810oC. Furnace temperature is 1700oC

Temperature sensor. 1 pc. long life B-type thermocouple and thermocouple extension assembly.

Sealing Flange: One set of metal flanges consisting of a 3-part metal assembly, and 2 pcs of O-rings for sealing hermetically the 50mm muffle ceramic tube at the bottom open end. Flange is equipped with water cooling passages and fittings - ready to accept any water-cooling system if needed.

Ceramics (alumina 99.6% purity):
1 pc. crucible: OD=40 mm, L=95mm, V=98 cc net; load is ~1,140 cts
- 6 pcs dishes: OD=30 mm, H=16 mm, V= 6 cc net; load is ~40 cts
Tube (muffle): 1 pc COE (Close One End) OD=50 mm, L=280 mm

Refractories (alumina 99.6% purity: 1 pc. reticulated alumina inserted in the muffle tube for holding the crucible.
Vacuum package: 1 pc pump (3.6 m3/h, 5 Pa, 150 W), 1 pc vacuum gauge, fittings and vacuum hose, solenoid valve and vacuum gauge. The vacuum assembly is used in conjunction with the muffle tube.

Full atmosphere control. Includes the following: two 150 mm flow flow-tubes, two pressure gauges, two pcs on-off valves, two pcs one-way gas valves for purging directly into the muffle selected gas ( nitrogen, oxygen), or any mixture of nitrogen-oxygen, or selected mixture of forming gas (hydro-nitro) for fully controllable atmosphere conditions to max. 1700oC. It can be used with half-muffle or with full-muffle tube.

Main temperature programmer-controller: Single program, auto tune, 51-segment (steps), auto PID artificial intelligence temp. programmer-controller
Gas exhaust assembly. This assembly consists of one gas moisture filter, one bubbler and 0-3 psig back-pressure gauge, indicating that the purged gas is exhausted via the bubbler.
Consumables and life expectancy of the parts


Electricity consumption depends on many factors. On a typical heating process the furnace requires less than 900 Watts to maintain 1700oC furnace soaking temperature for several hours.


A typical muffle tube lasts usually 12-15 runs if properly sealed at soaking furnace temperature about 1625oC in air; life expectancy is reduced proportionally as the furnace temperature is increased; 8-10 runs in vacuum at 1500oC for 2 hours
The life expectancy of technical ceramics (crucibles, disk, dish) depends on many factors (heating up rate, cooling down rate, soaking temperature, time are soaking temperature, type of fluxes and other additives is used. Technical ceramics usually last 10-12 runs at soaking 1700oC for several hours.
B-type thermocouple assembly lasts over 200 runs at 1700oC furnace temperature.


The life expectancy of the heating elements depends on many factors which should be carefully considered.; Best performance and longivity is heating between 1200oC to 1700oC (air, oxygen, other gases), max.1500oC (vacuum) No guarantee is given by any heating element manufacturer around the world on element brakeage. However, experience shows that more than 20 heating runs may be performed at 1700oC soaking time 10-70 hours/run before an element breaks or damaged. Generally, the estimated life expectancy for each element is about 1,500-1600 hours. If an element breaks is should be replaced without requiring to change all the other elements in the furnace.
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