NOTE. 

 Internal lacquering of tlns for jam. 



The following Note was written in reply to a query from a 

 business firm ; it embodies experience obtained at the Government 

 Cannery. It forms an addendum to paragraph 44 of the Fisheries 

 Bulletin entitled "Remarks on Canning." 



2. The " difficulty " mentioned is doubtless the blackening of 

 certain jams with, possibly, the acquirement of a slight chalybeate 

 taste. This is due to the action of the fruit acids on the metal, 

 principally, if not entirely, on the steel of the " tin-plate " ; some 

 fruits are particularly acid, and certain of the acids are more 

 active than others in this way; hence the protection of the metal 

 is absolutely necessary. 



3. The first thing then, is to use only tin-plate coated with a full 

 Quantity of tin. It is astonishing what differences exist ; some 

 cheap tin-plate is so thinly coated that the least corrosion or hard 

 usage removes the tin and exposes the steel to the action of the 

 acid. Jam manufacturers should specify a high quality coating 

 when ordering tirl-plate, of so much pure tin to the square inch. 

 This is the first precaution, without which even lacquering may 

 fail of its full purpose. 



4. Inside lacquering has long been practised at the Government 

 Fish Cannery for prawns— which are discoloured by naked tin- 

 plate — and fish with vinegar, and it has always been open to 

 enquirers to obtain information there and drawings of the plant. 

 The method is simple enough, yiz. — 



(l) Obtain a good oil varnish ; 



{2) Apply it, eicher as it is, or thinned with turps, or thickened 

 with boiled linseed oil, to the inside of the can ; 



(3) Bake the can at a certain temperature in a stove ; 



(4) Repeat the process. 

 Hence the questions are — ■ 



(1) What class of varnish is desirable .'' 



(2) Whether it should be thinned or thickened or even mixed 

 with a solid material or pigment ? 



(3) What sort of a stove is required and what should be the 

 temperature of stoving ? 



(4) What methods and precautions are necessary ? 

 IS 



