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Venetian Borax: Refining Tincal with Lime
Ra'ike (see also: de:Benutzer:Ra'ike) (Wikimedia Commons) · CC BY-SA 3.0
Charlie

Created by

Charlie

13. October 2026DE
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Venetian Borax: Refining Tincal with Lime

Native borax, tincal, came to Europe from the dried lake shores of Tibet and India coated in an earthy, soapy fat. Venice, then the Dutch, refined it in secret: the refined salt was called Venetian borax. One of their methods is recorded by Knapp, as Muspratt gives it in 1860: soften the tincal with water and a little slaked lime, wash it clean, dissolve it hot with a little chloride of calcium to take out the last of the soap, then crystallise it in lead-lined wooden cones. Borax is the flux of brazing and soldering.
Intermediate
Several days

Instructions

1

Weigh the tincal and the additions

Weigh the tincal, about 1 per cent of its weight of slaked lime, and about 2 per cent of chloride of calcium (step 7 works it out for 10 kg).

Materials for this step:

Tincal (Crude Borax)Tincal (Crude Borax)10 kg
Lime (Calcium Hydroxide)Lime (Calcium Hydroxide)100 g
Calcium ChlorideCalcium Chloride200 g

Tools needed:

Balance ScaleBalance Scale
2

Soften it with water and lime

Soften the tincal in a small quantity of cold water in a wooden tub, and stir it about while adding the slaked lime little by little.

Materials for this step:

WaterWater1 as required

Tools needed:

Wooden TubWooden Tub
Wooden PaddleWooden Paddle
Chemical Splash GogglesChemical Splash Goggles
Rubber GlovesRubber Gloves
3

Wash it several times

Pour off the turbid lime-water. Let the impurities settle out of it, then pour the clear liquid back over the crystals. Repeat this several times; it takes away the greater part of the soapy crust.

Tools needed:

Wooden TubWooden Tub
Wooden PaddleWooden Paddle
4

Dissolve hot with chloride of calcium

Dissolve the washed crystals in hot water and add the chloride of calcium. It turns what soap remains into an insoluble lime soap (and common salt); strain that off.

Materials for this step:

WaterWater1 as required
CharcoalCharcoal1 as required

Tools needed:

Evaporating PanEvaporating Pan
Charcoal FurnaceCharcoal Furnace
StrainerStrainer
Wooden PaddleWooden Paddle
Chemical Splash GogglesChemical Splash Goggles
Rubber GlovesRubber Gloves
5

Boil down to 21 degrees Baumé

Evaporate the clear liquid to 21 degrees Baumé, a specific gravity of 1.17, checking with a hydrometer.

Materials for this step:

CharcoalCharcoal1 as required

Tools needed:

Evaporating PanEvaporating Pan
Charcoal FurnaceCharcoal Furnace
HydrometerHydrometer
6

Crystallise in lead-lined cones

Run the liquor into wooden vessels lined with lead and shaped as short inverted cones, and let it crystallise. Any deposit collects in the narrow lower part and does not spoil the crystals. Knapp adds that a little tincal stirred in before this last crystallisation keeps the crystals from splitting and flying off the work when heated for soldering.

Tools needed:

Crystallising TankCrystallising Tank
Lead SheetLead Sheet
7

Knapp's additions, per 10 kg

Loading Jupyter Notebook...
8

Powder it for flux

Take out the crystals, dry them and grind them in a mortar to a powder for use as flux. Keep it covered: in dry air borax slowly loses water and turns opaque on the surface.

Tools needed:

Mortar and PestleMortar and Pestle
9

Troubleshooting

Borax refining troubleshooting.

Flow

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10

History and honest limits

Muspratt (1860) gives Knapp's two known methods of the secret Venetian and Dutch refining; this is the lime method. The other washed the powdered tincal with caustic soda lye and added carbonate of soda. By Muspratt's time most borax was made instead from the boracic acid of Tuscany and carbonate of soda. Knapp's per cent figures do not say of what; we take them as per cent of the tincal. Grinding the crystals to powder is ours.

Materials

5

Tools Required

12

This blueprint makes

Thumbnail
Placeholder

Borax Powder

Free

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