In a preferred method according to the invention, step  (S-1) takes place at a temperature in the range from 90 to 20  160°  C., preferably at a temperature in the range from 100  to 150°  C.  of its polymers, such as trioxane or paraformaldehyde, the  use of paraformaldehyde being preferred according to the  invention.  Additionally, apart from formaldehyde, other aldehydes  can also be used. Suitable aldehydes are for example acet- aldehyde, propionaldehyde, butyraldehyde, acrolein, croton› aldehyde, benzaldehyde, salicylaldehyde, cinnamaldehyde,  glyoxal and mixtures of these aldehydes.  Particularly preferred organic acids with a pKa value in  the range from 3 to 5 at 25°  C. are selected from the group  consisting of benzoic acid, lactic acid, citric acid, phthalic  acid, 2,4-dihydroxybenzoic acid and salicylic acid, wherein  benzoic acid, lactic acid, and citric acid are more preferred,  and benzoic acid is most preferred.  In step (S-1 ), a pH value is preferably established in the  range from 2.8 to 5, preferably in the range from 3.5 to 4.5,  in each case measured at 20°  C.  A preferred mixture according to the invention ( as defined  above), preferably in one of the embodiments characterised  as preferable, is a mixture that is producible by a method  according to the invention, preferably in one of the embodi› ments characterised as preferable.  The invention also relates to a method of production of a  mould or a core, preferably a no-bake mould or a no-bake  core for producing metal objects, comprising the step:  In a preferred method according to the invention the total  amount of furfuryl alcohol used is at least 50 wt. %,  preferably at least 55 wt. %, and is preferably in the range  from 60 to 75 wt.%, more preferably in the range from 62  to  72  wt. %, wherein the percentages by weight are relative  to the total weight of the resultant mixture according to the  invention.  US 9,993,863 B2  24  23  In a preferred embodiment for carrying out the no-bake  process, the refractory moulding base material according to  the invention ( constituent (iii) of a reaction mixture accord› ing to the invention) is first coated with the acid hardener  ( constituent (ii) of a reaction mixture according to the  invention). Then the binder (i.e. a mixture according to the  invention; constituent (i) of a reaction mixture according to  the invention) is added and, by mixing, is uniformly dis› tributed on the grains of the refractory moulding base  material already coated with the catalyst. The moulding  mixture can then be formed into a moulded article. Because  the binder and the acid hardener are uniformly distributed in  the moulding mixture, curing takes place substantially uni› formly even with large moulded articles.  In a preferred method according to the invention, curing  preferably takes place in the absence of sulphur dioxide.  Preferably, for curing a mixture according to the invention,  a reaction mixture according to the invention is produced,  which then hardens directly. The statements regarding the  reaction mixture according to the invention apply corre› spondingly to the method according to the invention.  In the method according to the invention for producing  cores and moulds for the foundry industry, preferably a  moulding mixture is used that is suitable in particular for  producing large moulds and cores, wherein these moulds  and cores display reduced emission of harmful compounds  during casting.  The invention also relates to a mould or a core for  producing metal objects, obtainable by curing a reaction  mixture according to the invention, preferably in one of the  embodiments characterised as preferable.  In another aspect, the invention relates to the use of a  mixture according to the invention, preferably in one of the  embodiments characterised as preferable, as a cold-setting  binder, preferably as a no-bake binder in foundry practice, in  particular in the production of metal objects by a casting  process, wherein the curing of the binder preferably takes  place without the use of gaseous sulphur dioxide.  In another aspect, the invention relates to the use of a  mixture according to the invention or of a reaction mixture,  preferably in each case in one of the embodiments charac› terised as preferable, in a no-bake process for producing  metal objects, preferably in a no-bake process in which no  gaseous sulphur dioxide is used for curing, preferably in a  no-bake process without a gassing step.  The invention further relates to a kit, comprising  as a first component, a mixture according to the invention,  preferably in one of the embodiments characterised as  preferable,  as a second component, an aqueous solution of an acid,  wherein the acid has a pKa value below 2 at 25°  C.  The invention is explained in more detail below with  examples.  A preferred method according to the invention comprises  the following further steps:  (S-2) preheating of the (first) reaction mixture resulting from  step (S-1) to a temperature in the range from 40 to 90°  C.,  preferably in the range from 50 to 80°  C.,  (S-3) optionally adjustment of the desired pH value with an  inorganic base, preferably with an alkali metal hydroxide,  preferably NaOH and/or KOH,  (S-4) addition of one or a plurality of compounds that can  react with any formaldehyde still present ( or addition of  one or a plurality of compounds for reaction with any  formaldehyde still present), wherein these compounds are  preferably selected from the group of organic compounds  with one or a plurality of H$_{2}$N and/or HN groups and/or  the group of phenolic compounds,  (S-5) preheating of the reaction mixture resulting from the  preceding steps to a temperature in the range from 10 to  50°  C., preferably in the range from 15 to 40°  C.,  (S-6) optionally addition of further constituents, preferably  one, a plurality of or all of the constituents ( e ), (f), (g), (h),  G), (k), (m) and (n) as defined above for a mixture  according to the invention, preferably in one of the  embodiments characterised as preferable.  curing, preferably acid-catalysed curing, of a mixture  or  according to the invention, preferably in one of the  embodiments characterised as preferable,  curing of a reaction mixture according to the invention,  preferably in one of the embodiments characterised as  preferable,  wherein curing preferably takes place at a temperature  below 60°  C., preferably in the range from 0 to 50°  C.,  more preferably in the range from 10 to 40°  C., particu› larly preferably in the range from 15 to 30°  C.  Unless stated otherwise, all figures given refer to weight.  Abbreviations used: FA=furfuryl alcohol, AI=assessment  index.  The chemical and physical parameters of the resins are  compared in Table 1 below. The values given correspond to  average values, which are typical for the respective binder.  EXAMPLES 