Compo recipe for gilding work

[Andy Dingley]

A while ago there was a question on compo recipes, which I don't think we could find at teh time. Here's one from the Australian picture framing book I mentioned.

Composition (Compo)

The following is a basic compo formula on which there are a number of variations.

Take 250 gms Pearl glue (Pearl glue is a type of animal glue, as used by cabinetmakers) and soak it in 125 mls cold water for several hours. Heat in a double boiler to 700 C until liquid, then add 20 mls of glycerine and 10 gins of zinc oxide.

Heat 100gms of Rosin (crushed to powder) in a small pan. The Rosin (colophony) should melt at around 901 C. Add to the rosin 20 mls Venice Turpentine and 60mls Linseed oil, and mix well. Mix the melted Rosin etc. into the hot glue and stir well.

The compo can now be made by adding the combined contents above to

600-700 gms of whiting. There are several methods of doing this, the best is probably to place the whiting in a bucket or basin, then pour on the hot glue/rosin mixture.

Rub talcum powder on your hands (to prevent sticking), then work the mixture by hand until it has the consistency of glazing putty.

Work the compo into approximately six flat cakes, wrap them well in the kind of very thin sheet plastic used for storing food. Compo will keep in the freezer for around four weeks; defrost the compo for one hour before placing it on the steam tray to soften and press into moulds

You may wish to experiment with the formula for Compo. For example, try increasing the amount of pearl glue from 250gms to 290 gms in 125 mls of water. You might also try increasing the rosin from 100 gms to

150 gms.

Some understanding of what each ingredient is doing will help you adjust the basic formula.

(1) Linseed oil makes the compo soft.

(2) Rosin makes the mixture elastic.

(3) Venice Turpentine prevents cracking.

(4) The mixture of glue and water acts as a binder.

(5) Whiting gives body.

(6) Glycerine tempers the glue.

(7) Zinc Oxide prevents formation of mould.

[Minorite]

thank you for posting this andy bob

[Robert E. Lewis]

It's late and I'm sleepy, but is there a decimal missing in these melt temperatures? I get a conversion of almost 1300­°F for '700 C' and about

1650°F for '901 C'. Maybe I'm a pantywaist, but Dad always said never to try to knead with my hands anything hotter than the melting temperature of lead, talcum powder or no.

Robert (He of the beautiful, non-lead-kneading hands)

[JGS]

[Andy Dingley]

Sorry, my fault for not proofreading the OCR well enough. There should be some degree signs in there, not digits.

Try 70°C for glue and and 90°C for rosin

[Andy Dingley]

My electric double boiler (chem lab stirrer hotplate) goes to about

250°C, but needs to be used with a silicone oil. The element goes hotter, but the oil then starts to polymerise and turns to a rubber.

Unfortunately the next job I need it for is some more oil-dried boiled linseed, and that takes 4 hours at 270°C Back to the gas stove I guess

[J. Clarke]

I think perhaps there is some confusion over the term "double-boiler" then. When a cook refers to a double boiler he's referring to a cooking untensil consisting of two nested pots intended to be used with water in the bottom pot and whatever is being cooked in the top one. It has no pressurization and so cannot bring the contents of the upper pot to a temperature greater than the boiling point of water (at least not unless you let all the water boil out of the bottom).

I'm not familiar with any device commonly referred to as a "double boiler" that uses a silicone oil--could you provide a link to a description so that those of us whose only familiarity with the other kind can gain for ourselves some idea what you're using?

[Robert Bonomi]

No brainer ...

SAME kind of gizmo. just substitute the silicone oil for the water.

_any_ sort of stabilizing agent in the lower container makes it a 'double boiler'. temperature for the upper container is limited to the boiling point of 'whatever it is' that is in the lower container.