Prip’s Flux

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Nancy LT Hamilton

Last updated: 2/15/19, 7/28/17


Prip’s Flux Information

Prip’s Flux is a fire scale preventative.  It will not always prevent fire scale – but, it helps a bunch.  Prip’s flux is named after Jack Prip aka John Axel Prip (1922 – 2009), who was a jewelry instructor at the University of Rochester.  See my related web pages for more information on fire scale especially:  Oxidation, Flux, and Fire Scale Prevention (should add Fire Stain too!).  Prip’s flux is called a “Barrier Flux” because it acts as a barrier to oxidation.  Soldering flux, which enables your solder to flow, is called “Flow Flux”.  See the recipe below to make your own “Flow Flux”.

Prip’s flux is for fire scale prevention only.  You need to use flux at your joins for the solder to flow.

Safety – Wear a particulate (N95) mask when measuring and pouring the chemicals as they are powders and the dust will enter your lungs.  Don’t inhale fumes while boiling – vent them.  Wear chemical-resistant gloves if handling.  Eye protection is required too.  Purchase safety goggles that are chemical rated.

Alcohol-based Prip’s Flux.

Be aware that some Prip’s flux recipes call for the use of denatured alcohol instead of distilled water.

Denatured alcohol is highly flammable.  If you decide to try this version (I don’t recommend it) remove the container from the soldering area and be sure to keep your spray bottle away from the flame too!  It is advised to gently warm the piece, allowing the alcohol to evaporate rather than burning it off.

Do not boil the mixture, as in the water-based recipe, as it will catch on fire.

BTW, you can purchase premade Prip’s Flux, if you want to skip the hassle of making it:  Griffith’s Prip’s Flux.

The Recipe for water-based Prip’s:


1 quart or 4 cups of distilled water

½ cup or 4.23 ounces or 120 grams boric acid (H3BO3 )(available at pharmacies).

2.822 ounces or 1/3 cup or 80 grams T.S.P.  Ensure that your box of T.S.P. notes that it contains trisodium phosphate.  (Available at hardware stores too).

2.822 ounces or 1/3 cup or 80 grams borax – available at the grocery and probably, the hardware store.  I use 20 Mule Team Borax, which is 99% Borax and 1% trace elements.

This is generally a 3:2:2 mix with 3 being the boric acid and 2 the T.S.P. and Borax.

Boil mixture, stirring – adding more water if necessary until all powders are dissolved. Don’t breath in the fumes.  A note about this mixture:  boric acid (as well as the borax) needs to be stirred in boiling water in order to dissolve.  Stir frequently. Note that, eventually, the boric acid will reseparate from the water and need to be reheated and re-stirred.

It is important to spray this flux onto WARM metal.  So, heat briefly with the torch and spray until you have a fine layer of the mixture and there are no spots of bare metal visible.  You can apply your soldering flux and solder before spraying or after or not at all.

You can also dip the piece into the mixture or brush it on.  These methods are not ideal but, better than nothing.  When using the dipping method or brushing method, heat until the flux dries evenly.  Your goal is to just dry the flux and not to over or underheat it.  If you overheat the flux you will see it change color (golden or brown). If you underheat it, it will remain liquid in spots.  The metal should have a white, even coating when heated properly.

When the Prip’s is dry,  apply your soldering flux to the join being soldered and then the solder. Prip’s is not recommended as a flux because of the addition of the TSP.  See below for info on making boric acid-based soldering flux.

The flux will re-crystallize and can clog sprayers.  You can either reheat the flux or use a mouth atomizer to aid in application.

An atomizer will work better than a trigger-type spray bottle.  You want a fine spray.

Another method is to let the flux sit for a few days until crystals begin to form.  Pour off the liquid into the spray container and leave the crystals behind in the storage container.  If you are using a spray bottle or airbrush and the sprayer is clogged, transfer the mixture to another container and then thoroughly clean the spray container and spray mechanism with water – removing all crystals. Then pour the solution back in. If possible, store the spray mechanism separately so, that crystals don’t form in the hose, or alternately, pour the unused portion of flux back into the storage container when you are done and rinse the sprayer well – give the spray mechanism a few pumps in clear water to rinse out any of the solution.  This will avoid crystal buildup and blockage.

You can read more about Prip’s flux in Peter W. Rowe’s article at Ganoksin. Also, Deborah E. Love Jemmott’s page.

Mouth Atomizer   To use the atomizer, check out this video:  by Jo Toye and ArtAlternatives (to see the atomizer in action).  These videos are about using the mouth atomizer with paint but the concept is the same.

More on the materials used in Prip’s Flux

Borax (sodium borate, sodium tetraborate, or disodium tetraborate),  a very weak acid, is a natural compound derived from the element boron. Boric acid is converted from borax.

Borax too, like boric acid, doesn’t dissolve readily in water.  Hot water will help it to dissolve.

Boric acid (hydrogen borate or boracic acid), is an acidic version of borax.

TSP Is a moderate to strong alkaline product.  TSP causes moderate skin irritation and severe eye irritant.  If ingested, can cause burns to internal organs. MSDS.


Related web pages

Testing link 2/15/19

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